For the cryopreservation of human embryos this study was accomplished as a preliminary experiment. The purpose of this study is to obtain optimal cryoprotectant, addition and dilution method of cryoprotectant and cooling rate for raising survival of frozon and thawed 2-cell mouse embryos. Seeding was done at $-7^{circ}C$ and the straw contained embryos was plunged at $-30^{circ}C$ when the slow cooling was ended. Embryos those developed normally to blastocyst after in vitro culture for over 96 hours were regarded as survival ones. The survival was the rate of number of survival embryos against the recovered embryos. The results are followed : 1. The survivals were 6.3, 71.2 and 67.4% respectively, when Glycerol, DMSO and 1,2-Propanediol were used as cryoprotectant. 2. When sucrose was added in freezing solution, the survival was 69.0%. That was higher than the survival of embryos frozen without sucrose in freezing solution. The difference was not significant. 3. Addition and dilution of cryoprotectant by 4 stepwise raised the survival than by direct, but that was not significant. 4. When embryos were frozen by -0.3, -0.5 and $-1^{circ}C/min$ before plunged into $LN_2$, the survivals were 67.9, 78.0 and 37.0% respectively. The differnce was significant.