| Conventional Long Name: | Duchy of Świecie |
| Era: | High Middle Ages |
| Government Type: | Duchy |
| Life Span: | 1248/1264–1270 |
| Year Start: | 1248/1264 |
| Event Start: | Partition from the Duchy of Gdańsk |
| Event1: | Conquest of the Duchy of Lubiszewo |
| Date Event1: | 1269 |
| Event End: | Conqust of the Duchy of Gdańsk and re-establishment as the Duchy of Pomerelia |
| Date End: | 1270 |
| P1: | Duchy of Gdańsk |
| P2: | Duchy of Kuyavia |
| P3: | Duchy of Lubiszewo |
| S1: | Duchy of Eastern Pomerania |
| Religion: | Roman Catholic |
| Capital: | Raciąż (before 1264) Świecie |
| Today: | Poland |
| Official Languages: | Polish, Latin |
| Title Leader: | Duke |
| Leader1: | Mestwin II |
| Year Leader1: | 1248/1264–1270 |
Duchy of Świecie (Polish: księstwo świeckie) was a duchy in Pomerelia centred around Świecie. Its only ruler was duke Mestwin II of the Samboride dynasty.
The state was established between 1248 and 1264, with duke Mestwin II being given the lands by his father, Swietopelk II, from the Duchy of Gdańsk.[1] He was originally given the lands around Raciąż and Szczytno, and around 1264, he incorporated into his territories Świecie, conquered from the Duchy of Kuyavia, which become the capital of the state.[2] In 1269, it incorporated the Duchy of Lubiszewo, and the year later, in 1270, it conquered the Duchy of Gdańsk, uniting its lands into the Duchy of Pomerelia.[3]