The article considers the rooting of the institution of indeterminate sentences in the Soviet legal reality of the NEP period. The author draws on a variety of sources, including archival ones, explores normative acts, projects, opinions of the leaders of the penitentiary system of that period. Attention is paid to the opinion of the Soviet scientific community about the institution under study, which followed world trends in criminal law and considered it necessary to adopt foreign advanced ideas in Russia. On the basis of the materials studied, the author comes to the conclusion that during the NEP period, further prerequisites continued to take shape for the institution of indeterminate sentences to be fixed in the criminal and corrective labor legislation. At the same time, a different attitude of the leadership of the NKJ and the NKVD to the correction of the length of stay of convicts in places of deprivation of liberty was revealed. From the point of view of the leadership of the NKJ, such a correction undermined the significance of judicial verdicts. The leaders of the NKVD, on the contrary, attached great importance to the possibility of reducing the term or changing the conditions of the convict’s stay, depending on his social danger. In the second half of the NEP, there was a need to resolve the contradictions between departments and all the prerequisites were in place to finally introduce the institution of indeterminate sentences into the legislation.