Belaj (Italian: Bellai) is a small village and Baroque Castle in Istria County, Croatia, in the municipality of Cerovlje.

After the Uskok War (1615–17) in which was devastated castel St. Martin at Posert, the previous center of the estate, Daniel Barbo von Waxenstein built this castle in the vicinity as a new residence.

Today the castle is a registered monument of cultural heritage, privately owned, partially renovated and very well preserved.

Left and right of the residential palace in the same line are located farm buildings with basements, stables and barns, which are connected with the castle high surrounding walls.

On the ground floor is the chapel of St. Henry II, with baroque marble altar and painted altarpiece, tombstones of family Barbo and tombstones of noble families from Kršan, Kožljak and Paz transmitted in Belaj from St. Mary on Čepić lake after the closure of the Paulists monastery in 1783.