Regierungsbezirk Zichenau was a Regierungsbezirk, or administrative region, of the Prussian Province of East Prussia from 1939-45. It is also referred to as South East Prussia (German: Südostpreußen). The regional capital was Zichenau (Ciechanów).
The government region was created on 26 October 1939, out of Polish areas annexed by Nazi Germany during World War II.
The region had an area of 12,000 km² and a population of approximately 895,000, including 800,000 Poles, 80,000 Jews, and 15,000 Germans.
Regierungsbezirk Zichenau was dissolved in 1945 when East Prussia was overrun by the Soviet Red Army. The territory was then restored to Poland.