The Pistoia Mountains Astronomical Observatory (; obs. code: 104), also known as the San Marcello Observatory and the Pian dei Termini Observatory (), is an astronomical observatory in San Marcello Piteglio, Tuscany, central Italy.
The observatory uses a 0.4- and 0.6-meter Newton-Cassegrain telescope and is the home of the Gruppo Astrofili Montagna Pistoiese, a group of amateur astronomers known for its members Luciano Tesi (founder), Paolo Bacci, and the late Vittorio Goretti, Silvano Casulli and Vasco Cecchini.