This research was conducted to observe developmental capacity of the early embryos aggrigated to phytohemagglutinin-M(PHA-M) in the culture of mouse embryos in vitro. The results showed that the development of blastocyst increased to 2-celT >< 2-cell : 68. 9%, 4-cell 4-cell : 92.5% and 8-cell 8-cell : 97.3% in the aggrigated embryos of ICR mouse, and 2-cell 2-cell : 90.0%, 4-cell 4-cell : 93.9% and 8-cell 8-cell : 100% in the aggrigated embryos of two different strains (ICR CBA/J mouse). (Key words : aggrigated embryos, in vitro 2-cell block, phytohemagglutinin-M, blastocyst)