Old Synagogue in Plzeň, Romanesque Revival synagogue in Jižní Předměstí, Plzeň, Czech Republic.

The Old Synagogue in Plzeň is a rectangular New Romanesque building, 12 m high and 20 × 14 m in plan, set in the courtyard of Smetanovy sady 80/5. It has a single hall with a wooden coffered ceiling, a two-storey women's gallery on wooden pillars, and an external staircase on the north side that also serves as an emergency exit.

The foundation stone was laid on 17 June 1857 on a courtyard plot near what is now Smetana Park, and the synagogue was consecrated on 8 April 1859. It was built to plans by Martin Stelzer with Wenzel Weisner as collaborator for a community of 41 families. After the Great Synagogue opened in 1893 it was used as a storeroom, which spared it from destruction; a full restoration followed in 2010–2014.

The women's gallery on wooden pillars now holds a small exhibition on Judaism, and a clock is set into its western section. Since 2019 the synagogue has been part of the European Routes of Jewish Heritage, certified as a Cultural Route of the Council of Europe. Services of the Jewish Community of Plzeň still take place here.

The synagogue and the former shammes house, now holding the ticket desk, stand in a courtyard reached through a passage at Smetanovy sady 80/5 in Plzeň 3-Jižní Předměstí; a large green dot on the street marks the entrance. Visits are possible Sunday to Friday, but not on the Sabbath or Jewish holidays.

The synagogue's organ, built by C. L. Edenhofer of Regensburg in 1869, did not survive: its pipes were melted down during World War I. The building held 250 worshippers and stood hidden in a courtyard, out of direct view from the street.