The leaf extracts of Araucaria bidwillii Hook. (Araucariaceae) were evaluated for their cytotoxic effect invarious human cancer cell lines. Preliminary investigation by brine shrimp lethality assay indicatedthat LC50 value of various successive extracts were found to be less than 1000 µg/ml, where the ethylacetate extract showed maximum activity of less than 100 µg/ml. Further cytotoxic evaluation ofvarious leaf extracts of Araucaria bidwilli Hook was carried out in four different human cancer cell lines- acute myeloblastic leukemia (HL-60), chronic myelogenic leukemia (K-562), breast adenocarcinoma(MCF-7) and cervical epithelial carcinoma (HeLa). Cytotoxicity was assessed by trypan blue dyeexclusion method and 3-(4,5-dimethyl thiazole-2yl)-2,5-diphenyl tetrazolium bromide (MTT)reduction assay. From the present investigation it was found that the ethyl acetate and methanolextract of Araucaria bidwilli Hook was found to be more effective in leukemic cell lines and was lesseffective in MCF-7 and HeLa. The IC50 value of the ethyl acetate extract in leukemic cell lines wasfound to be 28.18 and 34.64 µg/ml and methanol extract was found to be 33.11 & 39.81 µg/ml. It canbe concluded that various extract from the leaves of Araucaria bidwillii Hook. posses cytotoxic activitytested in brine shrimps and various human carcinoma cell lines.