20th Infantry Division () was a unit of the Polish Army during the interbellum period, which took part in the Polish September Campaign. It was formed in 1920 from the reorganization of the 2nd Lithuanian-Belarusian Division. Stationed in Baranowicze and commanded by Colonel Wilhelm Andrzej Lawicz-Liszka. In the summer of 1939 it was moved west and became part of the Army Modlin. Its task was to defend the partly fortified area north of Mława, near the inter war border of Poland and East Prussia. The Germans who fought against the 20. at Mława gave it a nickname "Steel Division."