| Nationality: | Turkish |
| Strokes: | Butterfly stroke |
| Club: | Galatasaray Swimming |
| Birth Date: | 21 October 1996 |
| Birth Place: | Çanakkale, Turkey |
| Height: | 179 cm |
| Weight: | 66 kg |
| Show-Medals: | yes |
Nida Eliz Üstündağ (born 21 October 1996) is a Turkish swimmer specialized in butterfly stroke. She is a member of Galatasaray Swimming.
She was born in Çanakkale on 21 October 1996. After graduation from Ankara Atatürk High School, she entered Başkent University to study Psychology.
Üstündağ competed for Ankara University before she transferred to Galatasaray Swimming.
In 2014, Üstündağ competed in the girls' 50 m butterfly, 100 m butterfly and 200 m butterfly events at the Summer Youth Olympics in Nanjing, China. She took part at the 2016 European Aquatics Championships in London, United Kingdom and placed 44th in the women's 50 m butterfly event.
She earned a quota spot to compete for Turkey in the women's 200 m butterfly event at the 2016 Summer Olympics.