The Diocese of Zealand (Danish: Sjællands Stift) was a protestant diocese in Denmark which existed from 1537 to 1922. Apart from the island of Zealand, from which it took its name, the diocese covered Møn, Amager and various smaller islands. The island of Bornholm was included in 1560. The Faroe Islands as well as some other overseas territories were also part of the diocese. Roskilde Cathedral was the main church and the bishop resided in the Bishop's House in Copenhagen.
The Diocese of Zealand was established in 1537 replacing the Catholic Diocese of Roskilde following the Reformation of Denmark.
The until then Catholic Roskilde Cathedral remained the cathedral and the official residence of the bishop was in Copenhagen as had been the case for his Catholic predecessors, although now in the former city hall which became the new Bishop's House.
In 1922, the diocese was divided into the Diocese of Copenhagen and the Diocese of Roskilde. Harald Ostenfeld, the last Bishop of Zealand, continued as Bishop of Copenhagen while Henry Fonnesbech-Wulff became Bishop of Roskilde.