Objective : The aim of this study was to evaluate the influence of different media on blastulation, mean cell number, percentage of inner cell mass (ICM) of total cells and ICM : trophectoderm (TE) ratio in mice. Materials and methods: A total 552 two cell embryos were retrieved from ICR female mice (4 weeks old) at 48 hr after hCG injection (mated just after hCG injection) and cultured in MEM (n=276) or TCM (n=276) supplemented with 20% hFF. The grading of blastocysts from zona-intact (ZiB) to -escape (hatching and hatched, ZeB) was performed at 72 hours after culture. Total, TE and ICM cell numbers were analyzed by differential staining of blastocyst. Statistical analysis was performed using t-test with SigmaPlot-2001. P-values < 0.05 were accepted as statistically significant. Results: The blastulation rate in MEM ($64.9{pm}4.95%$) was significantly higher (p=0.0031) than that in TCM ($57.2{pm}5.22%$). No differences were found in the number of ZiB and ZeB between MEM ($31.9{pm}2.62$, $33.0{pm}4.58%$), and TCM ($27.2{pm}4.28$, $30.1{pm}4.58%$). A total 314 blastocysts (MEM=166; TCM=148) were stained differentially. Mean cell number of blastocysts was significantly higher (p=0.0002) in TCM ($73.1{pm}3.3$) than in MEM ($61.7{pm}2.5$). Differential staining was successfully performed in 155 blastocysts (MEM=77; TCM=78). The percentage of ICM was significantly higher in MEM than in TCM ($20.9{pm}1.3$ vs. $17.1{pm}1.2%$, p=0.0281). The ICM : TE ratio was higher in TCM than in MEM (1 : $4.85{pm}0.68$ vs. 1 : $3.78{pm}0.78$, NS). Conclusion: These results show that MEM increase the blastocyst formation and percentage of ICM of total cells comparing with TCM in mice.