An extremely potent antitumor neo-clerodane diterpene was isolated from the oleoresin of the Brazilian medicinal plant, Copaifera lungsdqii Desfon. This compound was identified as (-) kolavenol 1. The antitumor effect of 1 against IMC carcinoma as determined from the increase in lifespan (I.L.S.) in mice was twice that of 5FU. The structure elucidation and the antitumor activity of the other related compounds 2-6 in this oleoresin were also described