The aim of the article is to define the tendencies of elaboration of ethical problems in early medieval exegetical texts - treatises of post-canonical Abhidharma. Ethics as a specific philosophical discipline concerning morals was not specifically developed because of cosmological character of Buddhist philosophy. Explication of the ethical discourse presented in treatises of eminent early medieval Indian Buddhist exegetics Vasubandhu (4-5 cc.), Asaṅga (4 c.) and Yaśomitra (8 c.) showed that specific for ethics questions on the highest good, sense of human life, the nature and sources of morals, freedom of will etc. were solved in post-canonical period. According to the religious doctrine they interpreted the highest good as the benefit of liberation ( mokṣabhāgīya ) from the fetches of suffering. The Buddha’s moral instructions known as prātimokṣa is aimed at the attainment of the highest good. Therefore the essence of morality has nothing to do with saṃsāra, and human society forming and perishing in cosmic cycles cannot be the source of moral norms. According to historiosophical myth, human beings get the first instructions on righteous behavior in deep antiquity from charismatic Universal ruler ( cakravartin ) coming to the world as the forerunner of the Buddha. He explains ontological contrariness of the good and the evil but is not the Teacher of the truth. Freedom of will cannot manifest itself spontaneously in a human being attached affectively to saṃsāra. Such an individual falsely takes his ignorant self-will for the freedom of will. Hearing the sermons of salvific teaching is the condition for the rising of free will impulse.