The Cathedral Basilica of the Assumption (or Pelplin Abbey) is a former Cistercian abbey, located in Pelplin, Poland, to the south of Gdansk. It was founded in 1258 by Sambor II, Duke of Pomerania, as "Samboria", and was a daughter house of the Cistercian Doberan Abbey. Work on the Brick Gothic building (length 80 m, height 26 m) began in 1289. The church was finished in 1323; additional work was completed in 1557.

The Cathedral is one of the largest brick Gothic temples in Poland. It has Gothic, Renaissance and Baroque interior decorations from the 15th to 18th century wih numerous side altars, stalli ensemble, pulpit and side pipe organs, among others. Its monumental late-Renaissance high altar (25-meter high) is Poland's largest and is believed to be the largest timber altar in Central Europe.

The monastic buildings contain Gothic frescoes (15th c). The Diocesan Museum houses a rich collection of sacral art, including a Gutenberg bible printed in 1453 and two Gothic figures of Our Lady.

The former Cistercian monastery complex, whose main part is the cathedral, is the core of the present Pelplin town.