The border of the Kazakh(Kyrgyz) ASSR with Siberia was formed in the early 1920s in difficult political and economic conditions. In those years, Kazakhstan had the opportunity to restore its territorial integrity. The article deals with the delimitation of the northern and north-eastern borders of the Republic in 1917-1922. Through the collection and study of archival materials and historiography, the authors make a detailed analysis of the process of creating the border between the RSFSR and the Kazakh(Kyrgyz) Republic. The article also reflects the complex relations of Sibrevkom, Kazrevkom, Moscow, BOAC and local authorities in the field of delimitation. Since the definition of borders is a complex process, there were several disputed territories. Detailed information on the work of the special commission established to resolve these disputed territories is given