The Diocese of Strängnäs (Swedish: Strängnäs stift) is a part of the Lutheran Church of Sweden and has its seat in Strängnäs Cathedral in Strängnäs, south of Lake Mälaren. The diocese is made up of the two provinces Närke and Södermanland (except for eastern Södermanland, which belongs to Stockholm County and the Diocese of Stockholm).
The diocese was first a Latin Catholic suffragan of the then Danish Diocese of Lund, which in 1104 was elevated to an archdiocese and became the Metropolitan see of all of Scandinavia. From 1164 on Strängnäs was suffragan to the Swedish archbishop of Uppsala. It was established during the 12th century by the English missionary Saint Eskil.