Nilsen is a surname of Norwegian origin, meaning "son of Nils". It refers to:
- Adolf Nilsen (1895–1927), Norwegian Olympic rower
- Alfred Nilsen (1892–1977), Norwegian politician; served one term in the Storting 1950–54
- Alfred Sigurd Nilsen (1891–1977), Norwegian politician; served three terms in the Storting
- Anders Nilsen (contemporary), American artist and novelist
- Arne Nilsen (b. 1924), Norwegian government minister
- B. J. Nilsen (b. 1975), Swedish sound artist
- Betty Ann Bjerkreim Nilsen (b. 1986), Norwegian orienteering competitor and cross country skier
- Dennis Nilsen (b. 1945), Scottish serial killer
- Einar Nilsen (1901–1980), Norwegian Olympic boxer
- Elin Nilsen (b. 1968), Norwegian Olympic skier
- Erling Nilsen (1910–1984), Norwegian Olympic boxer
- Harald Christian Strand Nilsen (b. 1971), Norwegian Olympic skier
- Ida Nilsen (contemporary), Canadian singer and songwriter
- Inge Nilsen (b. 1978), Norwegian professional football player
- Jeanette Nilsen (b. 1972), Norwegian Olympic handball player
- Jimmy Nilsen (b. 1966), Swedish motorcycle speedway rider
- Kristoffer Nilsen (1901–1975), Norwegian Olympic boxer
- Kurt Nilsen (b. 1978), Norwegian pop/country singer
- Laila Schou Nilsen (1919–1998), Norwegian Olympic skater and skier
- Lars Arvid Nilsen (b. 1965), Norwegian shot putter
- Lillebjørn Nilsen (b. 1950), Norwegian singer, songwriter, and folk musician
- Magne H. Nilsen (b. 1981), Norwegian professional football player
- Nils Emaus Nilsen (1886–1976), Norwegian politician; Served one term in the Storting 1950–54
- Oddvard Nilsen (b. 1940), Norwegian politician, served three terms in the Storting
- Olav Nilsen (b. 1942), Norwegian professional football player
- Ole-Jørgen Nilsen (1936–2008), Norwegian actor
- Oliver John Nilsen (1884–1977), Australian businessman and Lord Mayor of Melbourne
- Peder Nilsen (1846–1921), Norwegian government minister
- Phil Nilsen (b. 1985), English rugby union football player
- Roger Nilsen (b. 1969), Norwegian professional football player
- Rudolf Nilsen (1901–1929), Norwegian poet and journalist
- Rune Nilsen (1923–1998), Norwegian Olympic triple jumper
- Selmer Nilsen (1931–1991), Norwegian fisherman who spied for KGB during the Cold War
- Spencer Nilsen (contemporary), American video game music composer
- Steinar Nilsen (b. 1972), Norwegian professional football player and manager
- Tom-Christer Nilsen (b. 1969), Norwegian politician from Hordaland
- Torstein Aagaard-Nilsen (b. 1964), Norwegian music composer
- Vidar Nilsen (b. 1970), Norwegian-American science fiction writer
- Werner Nilsen (1904–1992), Norwegian-American soccer player