The early and late texts of the Russian psychologist and philosopher Sergei Rubinstein focus on ethical issues. The unfinished and fragmentary nature of these texts has contributed to the limited exploration of the ideas they contain. Rubinstein's main concern was the possibility of human moral improvement, a concern that originated in the young Rubinstein's study of the philosophies of Kant and Hegel, and somewhat later, the early manuscripts of Marx. In this paper, I show the pivotal importance of Kantian ethics for Rubinstein's theory of moral improvement. By criticising Kant's doctrine of the intelligible character of the human being, Rubinstein revises the relation between subjects and their deeds and shows that, in this relation, subjects not only express but also determine themselves. On the same basis, Rubinstein formulates the principle of creative self-activity, which he proposes to place at the foundation of a renewed 'Socratic-Platonist pedagogy' that can reveal the intersubjective nature of self-consciousness and will. In his critique of Kant, Rubinstein relies, to a large extent, on interpretations offered by Cohen, Natorp and Rickert. Rubinstein also attempts to solve Kant's problem of the dual nature of the human being, and in justifying the need to reconcile duty and inclination, he follows the same critical path as Schiller. Adducing the categorical imperative in its 'formula of humanity', and the principle of human self-determination through action, Rubinstein places the concept of "educating behaviour" at the core of his theory of moral improvement.