| Official Name: | Sundøy |
| Other Name: | Sundøya |
| Settlement Type: | Village |
| Pushpin Map: | Nordland#Norway |
| Pushpin Label Position: | right |
| Pushpin Map Caption: | Location in Nordland |
| Subdivision Type: | Country |
| Subdivision Name: | Norway |
| Subdivision Name1: | Northern Norway |
| Subdivision Name2: | Nordland |
| Subdivision Type3: | District |
| Subdivision Name3: | Helgeland |
| Subdivision Type4: | Municipality |
| Subdivision Name4: | Leirfjord |
| Utc Offset1: | +01:00 |
| Utc Offset1 Dst: | +02:00 |
| Postal Code Type: | Post Code |
| Postal Code: | 8890 Leirfjord |
| Coordinates: | 65.992°N 12.8586°W |
| Elevation M: | 62 |
| Elevation Footnotes: | [1] |
Sundøy or Sundøya is a village in the municipality of Leirfjord in Nordland county, Norway. The village is located about south of the village of Leland. Sundøya has a population of about 120 people. It is located on the north side of the Vefsnfjorden on the northeastern part of the island of Alsta, east of the Seven Sisters mountains, which isolate it from the rest of the island. Since Sundøy is surrounded by mountains and water, it was only accessible by boat until 2003 when the Sundøy Bridge was built, providing a road connection to the mainland of Leirfjord.