Nicasius was a Roman cognomen, whose variants include Nicasio, Nicaise, and Necaise. It can refer to:
Saints Nicasius of Rheims, martyr (5th century; feast 14 December) Nicasius of Dijon or Nicasius of Die (4th century; feast 20 March), bishop at the first Council of Nicea Nicasius, Quirinus, Scubiculus, and Pientia (3rd century; feast 11 October), martyrs; the first is sometimes identified as Nicasius of Rheims. Nicasius of Sicily (Nicasio Burgio, Nicasius Martyr, Nicasius de Burgio) (died 1187; feast 1 July), martyred Knight Hospitaller
Other Nicasio, California, a census designated place in Marin County Nicasius le Febure Nycasius de Clibano () Nicasius Russell (died 1646), goldsmith to Anne of Denmark Nicasio Silverio (born 1930), Cuban swimmer Nicasius, first bishop of Rouen () Alberto Nicasio (1902–1980), Argentinian artist Juan Nicasio (born 1986), Dominican baseball pitcher Nicasius de Vries (born 1995), Dutch racing driver Viviane Nicaise (born 1952), Belgian cartoonist and colorist