Nakai (written: 中井, 中居 or 仲井) is a Japanese surname. Notable people with the surname include:
- Asakazu Nakai (中井 朝一, 1901–1988), Japanese cinematographer
- Daisuke Nakai (中井 大介, born 1989), Japanese professional baseball infielder
- Hiroe Nakai (中井 広恵, born 1969), Japanese shogi player
- Hiroshi Nakai (中井 洽, 1942–2017), Japanese politician
- Hiroshi Nakai (中井 弘, 1839–1894), Japanese politician[1]
- Kazuya Nakai (中井 和哉, born 1967), Japanese voice actor
- Kie Nakai (中井 貴惠, born 1957), Japanese actress
- Kiichi Nakai (中井 貴一, born 1961), Japanese actor
- Masahiro Nakai (中居 正広, born 1972), Japanese singer, actor and host
- Masakazu Nakai (中井 正一, 1900–1952), Japanese aesthetician, film theorist, librarian, and social activist
- Masutaro Nakai (中井 増太郎, 1895–1969), general in the Imperial Japanese Army
- Nakai Chikuzan (中井 竹山, 1730–1804), Japanese politician
- Noémie Nakai (中井 ノエミ, born 1990), Japanese actress, director
- Norio Nakai (中井 紀夫, born 1952), Japanese writer
- R. Carlos Nakai (born 1946), Native American flautist
- Shogo Nakai (中井 昇吾, born 1984), former Japanese football player
- Takahiro Nakai (中井 貴裕, born 1990), Japanese judoka
- Takuhiro Nakai (中井 卓大, born 2003), Japanese footballer, known as Pipi
- Takenoshin Nakai (中井 猛之進, 1882–1952), Japanese botanist
- Takezo Nakai (中井 武三, born 1949), Japanese former handball player
- Yasuyuki Nakai (中井 康之, 1954–2014), Japanese baseball player
- Yoshikazu Nakai (中井 喜和, 1920–1991), Japanese mathematician, originator of the Nakai conjecture
- Yoshiki Nakai (中井 義樹, born 1983), Japanese football player
- Yoshinori Nakai (中井 義則, born 1960), Japanese artist
- Yuki Nakai (中井 祐樹, born 1970), retired Japanese shooto practitioner and mixed martial artist
- Yukino Nakai (仲井 由希乃, born 1996), Japanese badminton player
Nakai is a surname among the Navajo people of the American Southwest. Notable people with the surname Nakai include
- R. Carlos Nakai (born 1946) American musician, nominated for 11 Grammy Awards.