Cinnamic acid, also known as cinnamic acid, is an organic substance with the chemical formula of C9H8O2.

Cinnamic acid is a white to yellow crystal or crystalline powder with the fragrance of cinnamon oil and fruit. At atmospheric pressure, cinnamic acid has a boiling point of 300 degrees Celsius and a melting point of 133 degrees Celsius. It is insoluble in water and soluble in organic solvents.