The chloroform extract of the air-dried leaves of Coleus blumei afforded a mixture of diastereomers of a new abietane type diterpene whose structures were elucidated by extensive one and two dimensional (ID, 2D) NMR and mass spectrometry. Acetylation of the mixture afforded a single compound. Antimicrobial tests on the diterpene indicate that it is active against Bacillus subtilis, Pseudomonas aeruginosa and Candida albicans.