Abstract: To form tetraploid embryos,electric pulses were used to stimulate 2-cell blastomeres of Kunming mice.The pulses included combinations of four strengths (600,800,1000 and 1200 V/cm) and three durations (10,30 and 50 μs).Of the combinations,600 V/cm×50 μs and 1200 V/cm×30 μs produced the fusion rates of 91.6% and 93.0% respectively,and both were higher than the others.On the other hand,the pulses of 600 V/cm×10 μs and 1200 V/cm×50 μs did the rates of 58.9% and 60.2% respectively,being significantly lower than the others.The results showed that a certain pulse strength was necessary to achieve embryo fusion,and the duration was a key factor affecting the embryo fusion and its later development.What observed with a laser confocal microscope implied that the allocation,approach and fusion of nucleus was a spontaneous process in fused embryos.