Niels Nielsen
Niels Nielsen may refer to:
- Niels Nielsen (rower), Danish Olympic rower
- Niels Nielsen (sailor), Norwegian Olympic silver medalist in 1920
- Niels Kristian Nielsen, Danish gymnast at the 1920 Summer Olympics
- Niels Turin Nielsen, Danish gymnast at the 1908 and 1920 Summer Olympics
- Niels Erik Nielsen, Danish gymnast at the 1920 Summer Olympics
- Niels Nielsen (geographer), Danish geographer
- Niels Nielsen (mathematician), Danish mathematician
- Niels Nielsen (politician), Danish-born Australian politician
- Niels Åge Nielsen, Danish professor of Nordic languages
- Niels Nielsen, caretaker of the Old Man of the Mountain