Kastelruth (; ; ) is a (municipality) and a village in South Tyrol in northern Italy, about northeast of the city of Bolzano. It is one of ("The most beautiful villages of Italy").
As of 30 November 2010, it had a population of 6456 and an area of .
Kastelruth borders the following municipalities: Barbian, Campitello di Fassa, Völs am Schlern, Lajen, Urtijëi, Waidbruck, Ritten, Santa Cristina Gherdëina and Tiers.
The municipality contains the frazioni (subdivisions, mainly villages and hamlets) Seiser Alm (Alpe di Siusi), Pufels (lad. Bula, it. Bulla), Runggaditsch (lad. Roncadic, it. Roncadizza), St. Michael (San Michele), Seis am Schlern (Siusi), St. Oswald (Sant'Osvaldo), St. Valentin (San Valentino), St. Vigil (San Vigilio), Tagusens (Tagusa), Tisens (Tisana) and ÃÂberwasser (lad. Sureghes, it. Oltretorrente).
According to the 2024 census, 78.47% of the population speak German, 15.81% Ladin and 5.72% Italian as first language.