Martensen or Mårtensen is a surname. Notable people with the surname include:
Camilla Mårtensen (born 1970), Swedish politician Hans Lassen Martensen (1808–1884), Danish Luterhan bishop and academic Hans Ludvig Martensen (1927–2012), Danish Roman Catholic bishop Robert Martensen (1947–2013), American physician, historian and writer
See also Martinson Mortensen