Siror was a comune located in the Trentino province of the northern Italian region of Trentino-Alto Adige/Südtirol. Situated approximately 60 kilometres east of Trento, the municipality covered an area of 75.1 square kilometres and had a population of 1,244 as of December 31, 2004.
On January 1, 2016, Siror was merged with the municipalities of Fiera di Primiero, Tonadico, and Transacqua. This administrative merger resulted in the formation of a new municipality known as Primiero San Martino di Castrozza.