Belaj (Kozljak, Italian: Bellai) is a small village and Baroque Castle in Istria County, Croatia, in the municipality of Cerovlje. Castle Belaj is a registered Historical Heritage. Castle Belaj historically has numerous hectares of vineyard. In 2017 Belaj Castle opens to the public. In 2011, the population of the village is 16. In the vicinity of the village is another castle Posert.