Siror (Siror in local dialect) was a comune (municipality) in Trentino in the northern Italian region Trentino-Alto Adige/Südtirol, located about east of Trento. As of 31 December 2004, it had a population of 1,244 and an area of . It was merged with Fiera di Primiero, Tonadico and Transacqua on January 1, 2016, to form a new municipality, Primiero San Martino di Castrozza.
The municipality of Siror contains the frazioni (subdivisions) Nolesca and part of San Martino di Castrozza.
Siror borders the following municipalities: Canale d'Agordo, Predazzo, Canal San Bovo, Mezzano, Imer, Tonadico and Transacqua.