A new abietane diterpene, 16-acetoxy-7α,12-dihydroxy-8,12-abietadiene-11,14-dione, has been isolated from the acetone extract of the root of Plectranthus hereroensis and its structure established by spectroscopic means. This compound showed antibacterial activity against Staphylococcus aureus and Vibrio cholerae, and antiviral activity against Herpes simplex type II.