The Cathedral of St. John the Baptist () is a Roman Catholic cathedral located in Fira, on the island of Santorini, in the South Aegean region of Greece. The cathedral church serves as the seat of the Bishop of Santorini.
The cathedral is located in the city center, in the Catholic neighborhood.
The Baroque Revival-style structure of blue-gray and cream, was built in 1823 and was completely restored and rebuilt in 1970, after the earthquake of 1956.