Environmental safety on transgenic animals is often a controversial issue within the researchers and the public. Here, a total of 12 full-sib transgenic mice expressing enhanced green fluorescent protein (eGFP) were used for assessing foreign gene expression by single-line passage method and evaluating effects on GE gene with the environment with a total of 12 full-sib mice (positive: control = 6:6, with the same size of male and female mice). PCR method and fluorescent protein observation system (FPOs) were used for detecting the inserted exogenous genes in these mice. The results showed that the expression level of eGFP and WRPE gene (vector sequence) were not significantly different, but it significantly reduced by F1 to F4 generation (F1, F2, F3 and F4) (P < 0.05) by Real-time quantitative PCR (RT-qPCR). The effect of GE mice on the environment with 4- or 8-week-old full-sib transgenic mice offspring was evaluated. The exogenous genes were not detected by PCR in the mice manure. Microbial flora of transgenic mice were not significantly different with those of the control group (P > 0.05), neither male or female, at 4 or at 8 week-old. In addition, there was no significant difference of the microbial communities in mice gut as assessed by PCR-DGGE or by 16S rDNA sequencing between positive and control transgenic mice offspring. Furthermore, the phylogenetic analyses showed that the manure bacteria sampled during each of the 2 stages belonged primarily to 3 groups, Firmicutes, Bacteroidetes and Actinobacteria. No unknown microbial flora were found in the mice manure. [Supported by the National Natural Science Foundation of China (No. 31172195), the Fundamental Research Funds for the Central Universities(No: XDJK2014A010) and the 2013 Innovation Team Building Program in Chongqing universities (KJTD201334).]