Borgosesia is a comune (municipality) in the Province of Vercelli in the Italian region Piedmont , located about 80 kilometres (50 mi) northeast of Turin and about 45 kilometres (28 mi) north of Vercelli.

The largest town in Valsesia , it is crossed by the Sesia River.

The town was founded in 14 BC by the native population, and later was called Seso by the Romans after their conquest. In the Middle Ages it was owned by the Dukes of Biandrate and, in the 17th century, by Spain.