| Official Name: | Sundbyfoss |
| Settlement Type: | Village |
| Pushpin Map: | Vestfold#Norway |
| Pushpin Label Position: | top |
| Pushpin Map Caption: | Location of the village |
| Subdivision Type: | Country |
| Subdivision Name: | Norway |
| Subdivision Name1: | Eastern Norway |
| Subdivision Name2: | Vestfold |
| Subdivision Type3: | District |
| Subdivision Name3: | Jarlsberg |
| Subdivision Type4: | Municipality |
| Subdivision Name4: | Holmestrand Municipality |
| Utc Offset1: | +01:00 |
| Utc Offset1 Dst: | +02:00 |
| Area Total Km2: | 0.47 |
| Population As Of: | 2024 |
| Population Total: | 562 |
| Population Density Km2: | 1195 |
| Postal Code Type: | Post Code |
| Postal Code: | 3092 Sundbyfoss |
| Coordinates: | 59.5119°N 10.1257°W |
| Elevation M: | 80 |
| Elevation Footnotes: | [1] |
Sundbyfoss is a village in Holmestrand Municipality in Vestfold county, Norway. The village is located along the lake Hillestadvannet, about south of the village of Hof. The village of Gullhaug lies about to the southeast and the town of Holmestrand lies about to the southeast. The village of Hvittingfoss in Kongsberg Municipality lies about to the west. Hillestad Church lies about east of the village.[2]
The 0.47km2 village has a population (2024) of 562 and a population density of .[3]
Sundbyfoss is named after the local waterfall on the river Sundbyelva. The waterfall provided the basis for early industry in the village. Today, Sundbyfoss is mainly a residential area. The largest industrial enterprise is the "Haslestad Bruk" sawmill. Historically, the old private Tønsberg–Eidsfoss railway line and Holmestrand–Vittingfoss railway line both went through Sundbyfoss.