The article reveals the issues of penetration of the norms of Muslim law into the adat of the peoples of the North Caucasus. The preconditions for Islamization were an attempt to carry out a social revolution, which did not take into account a number of important features that had taken place in the relations between the social strata of the Caucasian societies.Along with this, comparative-comparative analysis of the penetration of Sharia into the customary law of the Kazakhs is conducted. The reasons of counteraction to violent introduction of the Muslim right by the people of the North Caucasus and advantages of the policy of the tsarist administration are revealed. The author of the article came to the conclusion that the criminal proceedings, as well as the system of crimes and punishments among the peoples of the North Caucasus, were based on the adat norms. At the same time, the penetration of the norms of Muslim law had a positive impact on raising the cultural and moral consciousness and eradicating inhuman institutions that existed in customary law. When forming political and legal thought in the adat reform, the nature of the Eurasian society was not taken into account and does not take into account, the peoples of the North Caucasus, which followed the rules of aristocratic and democratic rule, are inalienable representatives of this society.