Mayuri's appearance has a skeletal-like look to it with a skull-like visage. His face is painted entirely white with the inner portion of his face painted black with the exception of his nose. His eyes are a golden color and he constantly bares his teeth giving the appearance of him constantly smiling. Both his ears are seemingly replaced with stubbed golden cones. His fingernails are blue and, with the exception of the fingernail on his right middle finger, are all short. The one long fingernail is as long as the finger itself. He also wears a white hat with two ends that point to his right and a large purple scarf around his neck. His whole body, even his face and hands, has been painted black and white. He repaints his make-up every morning, as he always removes it before going to bed.
Without his makeup, Mayuri has blue hair and honey gold eyes. He has small, slatted portcullises with multiple earrings in place of where his ears would be, and his body is covered in scars.
Upon entering Hueco Mundo, Mayuri reveals a new look: his face paint had changed with him creating a black cross upon the center of his face covering everything but his nose and a small portion of his lower chin. His ear attachments have become shorter and rounder but wider, his chin has a long golden attachment reminiscent of an Egyptian Pharaoh beard, his teeth have become a golden color, and he no longer wears a hat as there is a golden frame around his face. His hair is also styled into "horns," that slope down from the top of his head and frame his face, which when viewed from the front looks much like a Pharaoh's crown.
17 months after Aizen's defeat, Mayuri displays another new look. The black face paint covers much of his face, leaving thin white lines going up his face and a white nose. He wears a long, golden headdress which curves back to his mid back. Underneath his chin are two opposite facing strands from the mask. On the backside of the headdress the Twelfth Division symbol is painted.
Following the first invasion by the Wandenreich, Mayuri dons a bright white overcoat with many ridges on the front. The overcoat also has a hood that has many protrusions that give the appearance of a sun. The shoes he wears has changed to be a plain white pair with the shoes splitting into opposite points at the toe.
110 years ago, Mayuri's appearance was similar to his current appearances, but with minimal details. He was still largely painted white except for the black paint which was arranged around his eyes like a large domino mask. He had gold cones covering his ears and blue hair combed back on the top of his head.
Mayuri Kurotsuchi is a researcher and personifies the stereotype of the mad scientist. By his early actions during the Ryoka Invasion, he is displayed as sadistic and cruel. He sees everyone and everything not as a living being, but as an object to be researched including himself. He has little respect or regard for most others, and was even willing to turn his own men (who were not aware of his plans) into living bombs in an attempt to capture Uryū Ishida and Orihime Inoue for experimentation. He also withheld vital information about the Bounts from the other Shinigami in order to capture one as a research subject for himself. However, while he usually shows disregard for life, he has been known to warn people of possible dangers when they present themselves. As a scientist, Mayuri despises perfection, as he believes that achieving such a state leaves him with absolutely nothing more to strive for namely imagination, knowledge and improvements which would result in nothing but despair; because of this, he derided Szayelaporro Granz for claiming to be a "perfect life form".
It is known that Mayuri's favorite food is pike fish, and that he does not like onion. One of his free-time activities is reading every character published in Seireitei Communication. He himself publishes a serialization in the journal, titled "Effective Medication for the Brain", which apparently contains detailed instructions on preparation of medicine and their application. Surprisingly, it is highly popular among the readers.
In battle, Mayuri likes to toy with his opponent, torturing them little by little until they can hardly stand. This was shown in both the fight with Uryū and his Espada counterpart Szayelaporro. Every time he fights he uses it as an experiment testing himself and his opponent little by little. He also uses it as an opportunity to implant microbes or other things in case they get away. Before engaging, though, he will make extensive research on his possible opponents to tilt the chance of winning in his favor. It is seen that, before the Winter War, he is busy reading in the library with a note on the door saying, "Enter and Die." He's shown to be doing this every time before he fights, against both the Bounts and the Espada.
While Mayuri holds life in disregard in favor of his research, he does believe in his duties as a member of the Gotei 13, and that all members of the organization are to be prepared to give up their lives in order to protect the Seireitei. To this end, he would gladly cut down any former comrades, even if they are under the enemy's control, test many of his experimental drugs on such comrades for the sake of his research which he believes to be the sake of the Seireitei, and even force his zombified fellow captains to become his minions to fight to their last breath for the sake of Gotei 13 and Soul Society, as opposed to killing them out of mercy.