Church of St. John the Theologian, Orthodox church in Saransk, Russia.

The Church of St. John the Theologian is a Russian Orthodox church in central Saransk, built in the Naryshkin Baroque style. The building rises in several tiers, with white walls covered in ornamental details that give the exterior a layered and decorative appearance.

The church was built in 1693 in Saransk's Streltsy sloboda, replacing an earlier wooden church. It was enlarged in the 18th century with side chapels, and the bell tower was added in the 1810s. Closed in the 1930s–1940s, it housed NKVD archives until reopening in February 1944 as the first active Orthodox church in Mordovia. It served as cathedral of the Saransk eparchy from 1991 until the consecration of St. Theodore Ushakov Cathedral on 6 August 2006.

The church is dedicated to St. John the Theologian, the name Russians give to the Apostle and Evangelist John. From February 1944 it was the first church reopened in Mordovia and long remained the only working Orthodox church in Saransk, so the parish carried the city's religious life through the late Soviet decades.

The church stands in the former Streltsy sloboda in central Saransk, a short walk from the city centre. It is an active parish church, so visits fit around services; it reopened for worship in February 1944 and has served the parish continuously since 2006, when the new St. Theodore Ushakov Cathedral was consecrated.

Naryshkin Baroque takes its name from the Naryshkin family, relatives of Peter the Great, who promoted this style in the years around 1700. The church in Saransk is one of the few examples of this style found outside the major Russian capitals.