The article examines previously unpublished letters of Siberian scientists from the family archive of the Kazakh scientist-encyclopedist academician Alkei Khakanovich Margulan. The scientific relations between scientists of Kazakhstan and Russia of the second half of the XX century, fundamental research and discoveries in the history of Kazakhstan are systematized. Introduced into scientific turnover 6 letters and 1 postcard from Academician, Doctor of Historical Sciences, Professor Alexei Pavlovich Okladnikov, who identified the local culture of the Paleolithic, Neolithic, Bronze and Iron Age in the steppes of Siberia, the Far East and Central Asia, who wrote many scientific papers on the culture of the first communal structure in these regions, And also 3 letters from Vitaly Epifanovich Larichev, archeologist, anthropologist, doctor of historical sciences, one of the leading specialists in archeology and history of ancient peoples of the Russian Far East and neighboring Manchuria and Mongolia, and 6 letters from Andrey Fedorovich Palashenkov, ethnographer, director of Omsk local history museum in 1943-1957. All these letters addressed to the academician A. Kh. Margulan are new data not published anywhere before. In addition, the study uses materials, memoirs and research from the personal fund of Academician A. Margulan in the Central State Archive of the Republic of Kazakhstan.