1-Octadecene is a long-chain hydrocarbon and an alkene with the molecular formula CH<sub>2</sub>=CH(CH<sub>2</sub>)<sub>15</sub>CH<sub>3</sub>. It is one of many isomers of octadecene. Classified as an alpha-olefin, 1-octadecene is the longest alkene that is liquid at room temperature.
Treatment of 1-octadecene with trichlorosilane in the presence of platinum catalysts gives octadecyltrichlorosilane. Octadecene adds to hydrogen-terminated bulk silicon.