The concept of ‘free will’ is central in both Kant’s and Schopenhauer’s moral philosophy. In the Kantian moral system, ‘free will’ is only regarded as moral when it dutifully follows reason and its a priori, absolute rules. Schopenhauer, on the other hand, holds that since human will is a priori to his reason, reason cannot engage will into any action. Instead of reason, he regards human motivations and stimulations as the main sources which shape any action, including moral actions. The important point is that he identifies three types of stimulations, namely ‘compassion’, ‘egoism’ and ‘pessimism’, among which he finds only ‘compassion’ to be the true stimulation for moral action and the basis of moral acts, and he dismisses the other two as immoral stimulations. He criticises foundations of the Kantian moral philosophy with the help of three following arguments: first, he questions the Kantian moral formalism and his a priori claims; second, he criticises the conceptual flaw in Kant’s moral philosophy (which is the result of an inconsistency between his claim that morality should be based on reason and his inner appreciation of verbal morality); third, he accuses Kant’s moral system of being one based on egoism. The present paper aims to explain the main status and characteristic of Schopenhauer’s moral system by way of explaining his criticism of Kant’s moral system.