Several laboratory studies have provoked widespread concern that Bt plants can harm non-target insects. A laboratory study was performed to investigate whether growth of Hylyphantes graminicola and Coleosoma octomaculatum as well as predation behavior of H. garminicola were affected by Bt cotton. Larvae of Helicoverpa armigera, preys for the spiders, were fed on Bt transgenic cotton hybrid (Zhongmian 29) or conventional cotton (Xiangza 3) respectively. The spiders were reared twice every week,the ekdysis of nymph of spider was obeserved every day and the body mass of adult spider was weighted when it matured. No significant difference in the development pattern and adult body weight (p>0.05) was detected between H. graminicola nymphs reared on Bt cotton fed H. armigera larvae and those on conventional cotton fed ones. Same conclusion was drawn from comparing the development and adult body weight of C. octomaculatum nymphs raised on Bt cotton fed H. armigera larvae with those raised on conventional cotton fed ones (p>0.05). The predation functional responses by adult H. graminicola which survived in feeding experiment to larvae of H. armigera which were fed with Bt cotton or conventional cotton was also carried out under laboratory conditions. We found that the predation functional responses by adult H. graminicola to larvae of H. armigera satisfied Holling II disc equation. Also predation behavior of adult H. graminicola was unaffected when they raised on Bt cotton fed H. armigera. In conclusion, Bt cotton didn’t cause harm to the spiders.