The article considers codification projects of criminal legislation, which have not been previously studied in legal science. The chronological framework of the study is substantiated. It covers the period from the late 1920s to the early 1930s. Codification consisted in drafting the Criminal Code. The article is based on various sources. First of all, the texts of the projects themselves were studied. Many of them were printed in separate brochures, accompanied by explanatory notes and commentaries. The process of discussing projects was reflected in specialized legal journals. In addition to published sources, archival materials from the funds of scientific institutions that participated in the preparation of projects were used. The main research methods were comparative legal (used to compare individual projects) and formal legal (used to analyze the content of the proposed rules). The conditions and reasons for the reform of the criminal legislation that was developed in the late 1920s are revealed. The following reasons are indicated and disclosed: political; law enforcement; legislative; doctrinal; legislative. Three main drafts of the Criminal Code are analyzed. The most famous was the project of N.V. Krylenko. The second project was prepared in a scientific institution - the State Institute for the Study of Crime and the Criminal. The third project was developed by the leaders and staff of the Supreme Court of the USSR. Similarities and differences of the projects are shown. All the projects reflected the influence of the sociological school of law. They proposed a simplified classification of crimes, replaced the concept of punishment, and, when imposing punishment, they recommended taking into account the class origin of the offender. When considering the case, the court allowed a wide judicial discretion. Krylenko's project was characterized as the most radical. Krylenko openly denied the domestic tradition of codifying criminal law. Each project was actively criticized. There was no constructive cooperation. The drafts did not become laws, but they influenced the change in criminal law in the 1930s, which turned into a means of solving political problems. A positive result was an attempt to holistically reform the sources of criminal law. A number of projects intended to unite in one law rules that had previously been dispersed in the laws of the USSR and the RSFSR. Studying the drafts of the Criminal Code fills the gap in knowledge about an important stage in the codification of Soviet legislation and the development of criminal law.