Nagai can refer to:
- The city of Nagai, Yamagata in Japan
- Takashi Nagai, a Nagasaki radiologist and prominent Japanese Catholic writer.
- An alternative name for Nagapattinam district, Tamil Nadu, India
- Go Nagai, a Japanese manga artist known for many breakthrough and controversial manga.
- Kenji Nagai, Japanese journalist, killed in Myanmar
- Kensuke Nagai, Japanese international footballer.
- Koji Nagai, Japanese businessman, CEO of Nomura Holdings.
- Ryo Nagai, Japanese footballer who plays for Cerezo Osaka and Perth Glory
- Nagai Kafu, a Japanese novelist, playwright, essayist, and diarist.
- Nagai Michiko, Japanese writer
- Nagai Sriram, Indian musician and Carnatic violinist
- Nagai Tatsuo, Japanese writer
- Yasutomo Nagai (1965–1995), Japanese Motorbike driver
- Nagai (Star Wars), a fictional alien race in he Star Wars franchise