A yellow oily liquid more viscous than water, cinnamaldehyde smells strongly of cinnamon.

Cinnamic aldehyde or cinnamaldehyde (more precisely trans-cinnamaldehyde, the only naturally-occurring form) is the chemical compound that gives cinnamon its flavor and odor.

Cinnamaldehyde occurs naturally in the bark of cinnamon trees and other species of the genus Cinnamomum like camphor and cassia. These trees are the natural source of cinnamon, and the essential oil of cinnamon bark is about 90% cinnamaldehyde.