The aim of this study, embedded in China National GMO Project of New Varieties, was to investigate the potential immunotoxicological effects of GM crops. The corn modified with Cry1Ah gene was developed by Institute of Plant Protection, China Academy of Agricultural Sciences Research. The Cry1Ah gene was cloned from the insecticidal protein genes of Chinese Bacillus thuringiensis isolate BT8. A plant expression vector pHUAh harboring the cry1Ah gene was constructed and transferred into the parental corn as described in Yue et al [9]. Coded protein Bt is a well-known insecticide to lepidoptera, diptera, and many other kinds of insects [10]–[11]. Bt can bind with the receptor of brush border membrane vesicles of insect's mid-gut, then lead to intestinal perforation, cell disintegrating and produce insecticidal action [12]. The parental corn used in this study has a long history of consumption in China, and there was no evidence of toxicity effects. In the study, corn flours from the GM corn and the parental corn were formulated into balanced basic AIN93G diets [13] at a proportion of 70%, then fed to BALB/c mice.