This research was performed to screen the cytotoxic activities of some pharmaceutical insect relatives. Cytotoxic activities of total extract and fractions of hexane, ethyl acetate, methanol, water and boiling water were extracted from four pharmaceutical insect relatives: the Chinese gall, the cicada slough, the hornet nest and the batryticated silkworm. These extracts were investigated against the cancer cell lines of L1210, P388 and SNU-1 in vitro tests. Results showed that, ED, , against the cancer cell lines of L1210, P388 and SNU-1 were 0.55, 0.50, and $0.83{mu}g/ml$ in the ethyl acetate fraction from the Chinese gall; 1.07, 2.19, and $2.24{mu}g/ml$in the ethyl acetate fraction, 1.51, 1.26, and $1.45{mu}g/ml$ in the water fraction and 1.48, 2.29, and $1.29{mu}g/ml$in the boiling water fraction from the cicada slough; 3.31, 2.00, and $6.61mug/ml$ in the water fraction from the hornet nest and 13.80, 19.95, and $31.62{mu}g/ml$in the hexane fraction and 33.88, 21.88, and $25.12{mu}g/ml$in the ethyl acetate fraction from the batryticated silkworm, respectively. All of the fractions mentioned above showed high cytotoxic activities and could be suggested for further studies in vivo tests.