The Krk Cathedral or fully Cathedral of the Assumption of the Blessed Virgin Mary (Croatian: Katedrala uznesenja blažene Djevice Marije or Krčka katedrala) is a cathedral in the town of Krk on the northern Adriatic island of Krk, Croatia. It is the seat of the Roman Catholic Diocese of Krk. The church was built in the 5th or 6th century but archeological evidence suggests that the site was used by Christians as early as 4th century.

The cathedral is located beneath the Krk town hill. The first documented mention of the church dates from 1186. It is a three-nave early Christian basilica which is part of a larger complex, along with the Romanesque Church of Saint Quirinus (12th century), a bell tower (16th century), the Chapel of Saint Barbara, an early Christian baptistry and an apse. As common with other churches from the same period, it is oriented east/west, with its façade facing a street which goes through the town of Krk in the north/south direction. The church is 40 meters long and interior width is 14.5 m (48 ft).

During several archeological excavations between 1956 and 1963 led by Andro Mohorovičić the ruins of an ancient Roman thermae dating from 1st century were discovered. Remains of a hypocaust and a tepidarium with a preserved mosaic floor tiling were uncovered. Large mosaic pieces worn out of people walking over them were found, which suggest that the site may have been used for Christian masses as early as the 4th century, before the cathedral was built.

According to historical records right next to the former tepidarium a Chapel of Saint John the Baptist with a baptismal font was later built, which stood there until 1565. This implies that one of the pools of the thermae has been converted into a baptistry. Beneath the floor of the present-day Chapel of the Holy Heart of Jesus a barrel-like piscina for baptismal water was also found.

The cathedral's present-day Romanesque design was created in the 11th and 12th century, around at the same time when its existence was first documented in 1186. Above the fourth interior capital (when counting from the south side entrance) there is an inscription dedicating the church to Virgin Mary, as it marks the place where the early Christian basilica used to end.