Cathedral of the Virgin Mary’s Immaculate Conception, Thessaloniki, Catholic cathedral in Thessaloniki, Greece.

The Cathedral of the Virgin Mary's Immaculate Conception on Frangon Street is a three-aisled basilica with a semicylindrical vault, designed by Italian architect Vitaliano Poselli and built between 1897 and 1899. Its interior has Corinthian colonnades, a statue of the Apostle Paul and stained-glass windows, and a 40-metre bell tower with a clock stands beside it.

The Jesuits built St. Louis Church here in 1742; it burned in the 1839 fire. A later church of 1867 was damaged in the 1897 fire, and the present cathedral, designed by Vitaliano Poselli, was begun in 1897 and completed in 1899. It became the seat of the Apostolic Vicariate of Thessaloniki in 1926.

Locals call it the Frangoklisia, the "Frankish church", after the Frangomahalas quarter around Frangon Street where Thessaloniki's European residents settled from the 19th century. Masses are celebrated in Greek and English, with Sunday services at 08:00 and 10:00 in Greek and 19:00 in English.

The church is located at Fragkon 19, nestled between taller buildings, so it can be easy to miss unless you look carefully for its entrance. Services take place regularly in the mornings, with specific times available through the cathedral's website.

A French tobacco merchant named Frederick Charnaud funded the cathedral's construction, while a Slovenian Lazarist brother named Michael Bucar decorated the crypt with artistic details. This unusual combination of French, Italian, and Slovenian influences shapes the interior character of the building.