This experiment was conducted to compare different procedures for improvement of viability of embryos after bisection and to investigate some factors affecting development of the bisected embryos. Demi-embryos were successfully produced by micromanipulation of mouse and goat embryos at stages from morula to blastocyst. In mouse, a superior viability(90%) of demi-embryos was achieved by culturing expanded blastocysts after bisection. The highest pregnancy rate(57.1%) and implantation rate(28.2%), which were almost same as the rates of intact embryos. were also achieved by transferring the demi-embryos at this stage after culture for 24 h in vitro. Twenty -eight 3%) of 30 embryos collected from superovulated Korean native goats were successfully bisected, of them 23 demi-pairs were transferred to recipients. Six and 3 does of them were diagnosed pregnant on 21 and 60 days of gestation, respectively. The present result indicates that in goat, hatched blastocysts might be more suitable for successful bisection to produce monozygotic twins than morulae or earlier blastocysts.