Blach is a surname, from Old High German translating to the English word "black". It can also be a typo or misspelling of "black". It can also be a Polish surname Błach. Notable people with the name include:

• Arne Blach (1900–1977), Danish field hockey player
• Ejvind Blach (1895–1972), Danish field hockey player
• Helena Blach Lavrsen (born 1963), Danish curler and Olympic medalist
• Niels Blach (1893–1979), Danish field hockey player
• Ty Blach (born 1990), American baseball pitcher
• Wiesław Błach, Polish judoka

• Black (disambiguation)
• Blachman (disambiguation)