Yew cortex, twigs and leaves(Florida yew, Taxus floridana Nutt et Champ; Pacific, yew Taxus brevifolia Nutt(Taxaceae)) were extracted with MeOH and $CHCI_3$, respectively, and then the chloroform extract was fractionated by silica column chromatography. As biologically active substances, taxol derivatives were identified and several biological activity tests were followed. The results showed that it bad no antimosquito activity and inhibited the growth of root meristem of cress seeds. The chloroform ext. of Florida yew showed 91%, inhibition rate at 400 ppm and the taxol fractions of Pacific yew did 91% at 200 ppm, 94% at 100 ppm. In the antitumor activity tests in vitro against a cultured cell line of L1210 mouse leukemia, Pacific yew showed 99% inhibition rate at 1.0 ppm and Florida yew did 97% at 10 ppm.