The purpose of this paper will be to study the attitude of Kant toward the principle of perfection as the basic moral principle. By perfection is meant here man's internal perfection, not general perfection, nor external perfection in the sense of God or the will of God. By Kant's attitude is meant first of all a brief historical sketch of the role of perfection in his pre-critical and critical ethics and secondly his criticisms of it. This paper will also attempt to evaluate Kant's criticisms to see whether they are valid criticisms and to see whether or not his own principle of the categorical imperative can escape the criticisms which he made against the principle of perfection.