Boljunčica is a river in inland Istria, Croatia. It discharges into the Adriatic Sea near Plomin.
It is 33 kilometres (21 mi) long and it has a basin with an area of 230 square kilometres (89 sq mi).
Its average discharge at the measurement station in Polje Čepić (covering 183 km2 of the basin) is 0.956 m3/s, and it can go completely dry.
Boljunčica rises on the western slopes of the Učka mountain and flows to the south. Near Polje Čepić and Potpićan, it goes underground and emerges near Plomin.
