Ambrosius or Ambrosios (a Latin adjective derived from the Ancient Greek word ἀμβρόσιος, ambrosios "divine, immortal") is a given name and a surname. Notable people with the name include:
- Ambrosius Alexandrinus, a Latinization of the name of Ambrose of Alexandria (before 212 – c.250), Egyptian theologian and saint
- Saint Ambrose (Aurelius Ambrosius) (c. 340–397), bishop of Milan
- Ambrosius of Optino (1812–1891), Russian Orthodox monk
- Ambrosius Gudko (1867–1918), Russian Orthodox saint and bishop
- Ambrosius Aurelianus, fifth-century war leader of the Romano-British
- Ambrosius of Georgia (1861–1927), Catholicos Patriarch of All Georgia
- Ambrosius, Metropolitan of Helsinki (born 1945), Finnish priest
- Ambrosius Beber (fl. 1610–1620), German composer
- Ambrosius Benson (c. 1495/1500 – 1550), Italian painter
- Ambrosius Blarer (1492–1564), Swiss reformer
- Ambrosius Bosschaert (1573–1621), Dutch painter
- Ambrosius Bosschaert II (1609–1645), Dutch painter, son of the above
- Ambrosius Brueghel (1617–1675), Flemish Baroque painter
- Ambrosius Ehinger (c. 1500 – 1533), German conquistador
- Ambrosius Francken I (1544–1618), Flemish Baroque painter
- Ambrosius Francken II (1590–1632), Flemish painter, nephew of the above
- Ambrosius Frobenius (1537–1602), Swiss printer and publisher
- Ambrosius Haingura (1957–2000), Namibian activist and politician
- Ambrosius Holbein (c. 1494 – c. 1519), German and Swiss painter, drawer and printmaker, elder brother of Hans Holbein the Younger
- Ambrosius Hubrecht (1853–1915), Dutch zoologist
- Ambrosius Lobwasser (1515–1585), German humanist and translator
- Macrobius (fl. 5th century), Roman grammarian and philosopher (Ambrosius Theodosius Macrobius in later manuscripts)
- Ambrosius Moibanus (1494–1554), German Lutheran theologian and reformer
- Ambrosius Pelargus (c. 1493 – 1561), German anti-reformer Dominican theologian
- Ambrosius Petruzzy (died 1652), Italian sculptor
- Ambrosios Pleianthidis, Greek Orthodox metropolitan bishop
- Ambrosius Stub (1705–1758), Danish poet
- Merlin, in Arthurian legend, named Merlin Ambrosius in Godfrey of Monmouth's Historia Regum Britanniae
- Ambrosius, a character in the film Labyrinth