| Conventional Long Name: | Masurian District |
| Native Name: | Okręg mazurski |
| Nation: | the Republic of Poland |
| Subdivision: | District |
| Date Start: | 14 March |
| Year Start: | 1945 |
| Date End: | 24 June |
| Year End: | 1946 |
| P1: | East Prussia |
| P2: | Reichsgau Danzig-West Prussia |
| S1: | Olsztyn Voivodeship (1946–1975)Olsztyn Voivodeship |
| S2: | Gdańsk Voivodeship (1945–1975)Gdańsk Voivodeship |
| S3: | Białystok Voivodeship (1944–1975)Białystok Voivodeship |
| S4: | Kaliningrad Oblast |
| Image Map Caption: | The administrative subdivisions of Poland in 1945, including the Masurian District |
| Title Leader: | Attorney-in-fact |
| Leader1: | Stanisław Piaskowski |
| Year Leader1: | 1945–1946 |
| Membership Title1: | Country |
| Membership1: | Provisional Government of the Republic of Poland (1945) Provisional Government of National Unity (1945–1946) |
The Masurian District, also known as the District of East Prussia, and designated as the 4th District, was a district that acted as an provisional administrative division of Poland, during the administration of the Provisional Government of the Republic of Poland in 1945, and the Provisional Government of National Unity from 1945 to 1946. It was centered around the areas of Masuria, Powiśle and Warmia.
It was established as one of four provisional districts on 14 March 1945.[1] [2]
On 25 September 1945, areas near its western border were incorporated into the Gdańsk Voivodeship, while the areas near its eastern border, to the Białystok Voivodeship.[3] In December 1945, the Polish administration in Iławka was expelled by the Soviets, and the town, which was originally supposed to belong to Poland with the original border set one kilometer north of the town, was annexed to the Soviet Union.[4] The Masurian District existed until 28 June 1946, when it was abolished and replaced with the Olsztyn Voivodeship.[5]
The head of the district was the attorney-in-fact Stanisław Piaskowski.[1]