To determine the effect of calcium on the preimplantational development of mouse two-cell embryo, the various concentrations of calcium were added into the culture media and the rate of blastocyst formation was observed. Also, to examine the effect of trifluoperazine, an inhibitor of calmodulin which is involved in the several intracellular calcium functions, embryos were cultured for 48 hours at the various concentrations of this inhibitor. An additional 24 hour culture was done to examine the effect of this drug on the transformation from morula to blastocyst. The results are as following ; 1. About 1.71mM of extracellular calcium is adequate for blastocyst formation and the higher concentrations of calcium (3.43mM and 8.55mM) do not affect on the blastocyst formation and the degenerating rate. 2. Trifluoperazine $100{mu}M$ presents the inhibitory effect on the blastocyst formation while $1{mu}M$ and $10{mu}M$ do not so. 3. After an additional 24 hour culture, there is transformation of morula to blastocyst and the degenerating rate of embryo is increased all together.