Tophane Fountain (Turkish: Tophane Çeşmesi) is a 18th-century public water fountain built by Ottoman sultan Mahmud I in the Ottoman rococo architecture and situated in the square of Tophane neighborhood in Beyoğlu district of Istanbul, Turkey. The sebil, a public fountain to provide drinking water for travellers and running water for praying people's ritual washing needs, was commissioned by Sultan Mahmud I (reigned 1730-1754). It was built in 1732, in an era with great importance attached to the construction of many fountains.
The fountain was built as a stand-alone structure in the type of a "square fountain" (Turkish: meydan çeşmesi). It looks like a monument, but contributes an architectural integration to the Kılıç Ali Pasha Complex (1580), which is situated nearby. It has the form of a square prism in general. However, the lower half of the structure has an octagonal plan, which transforms into a square at the upper half with the help of muqarnas.
It was designed by the court architect Kayserili Mehmed Ağa in the rococo architectural style of Ottoman Tulip Period (1703–1757). It is adorned with ornamentation showing a transition from classical to rococo style. Its design shows similarities with the Fountain of Ahmed III at Topkapı Palace (1729) and the Fountain of Ahmed III in Üsküdar (1729).