Sundbyfoss is a village in Holmestrand Municipality in Vestfold county, Norway.

The village of Hvittingfoss in Kongsberg Municipality lies about 8 kilometres (5.0 mi) to the west.

Hillestad Church lies about 3 kilometres (1.9 mi) east of the village.

[1] Sundbyfoss is named after the local waterfall on the river Sundbyelva.

The largest industrial enterprise is the "Haslestad Bruk" sawmill.