The article is devoted to the new historical investigations on the problem of the Polish-Soviet state border admittance in the former East Prussia in the years 1945-1958. The matter of the final course of the Polish-Soviet border was not resolved until years 1956-1957. The Soviet side proposed formal delimitation in the territory of the Polish-Soviet border in the region of the Kaliningrad circuit in April 1956 doing the condition of temporariness away. The border was traced in the territory according to its already existing course after months of works of the delimitation committee. The agreement confirming the course of the border was signed in Moscow on the 5th of March 1957.