It is suggested that carbohydrate metabolites may involve in the development of morula to blastocyst but many of the mechanisms are not unmasked. Two-cell stage embryos were collected and examined the effects of lactate on the development of blastocyst in vitro. The expression profiles of lactate dehydrognase (Ldh) genes and aquaporin (Aqp) genes were analyzed with RT-PCR. The successful development from morula to blastocyst was dependent on lactate concentrations. The expression profiles of Ldh genes were changed by the lactate concentration. Ldha was expressed in morula stage at 10 mM lactate, and in blastocyst stage at lactate free condition. Ldhb was expressed in morula stage at 10 mM and 20 mM lactate, and in blastocyst stage at 10 mM lactate. Aqp genes were also showed different expression patterns by the lactate concentrations. Aqp3 was expressed in hatching embryo at 120 hr post hCG administration (hph) which was cultured in BWW medium and lactate free condition. Aqp7 was expressed in hatching embryos at 120 hph which was cultured at 10 mM lactate condition. Also Aqp8 was expressed in hatching embryo at BWW and 20 mM lactate condition. Aqp9 was expressed in morula at BWW and 10 mM lactate condition, and in blastocyst at BWW. Based on these results, it is suggested that concentration of lactate in the medium and the level of lactate synthesis in embryo is critical factor for blastocoels formation. In addition it is suggested that LDH may involve the AQPs expression in embryos.