Kafu Nagai (?? ??, Nagai Kafu) was the pseudonym of the Japanese author, playwright, essayist, and diarist Nagai Sokichi (?? ??; 3 December 1879 – 30 April 1959).
His works are noted for their depictions of life in early 20th-century Tokyo, especially among geisha, prostitutes, cabaret dancers, and other denizens of the city's lively entertainment districts.