Abstract: Objective To improve the efficiency of electrofusion of reconstructed embryos derived from oocytes and fetal fibroblast cells both of B₆D₂F₁strain within a mouse somatic cell nuclear transfer（SCNT）program.Methods The effect of different pre-treatment on donor cells，fusion midia，electrical field intensity，electrodes’shape and cell passage on the efficiency of electro fusion was studied.Results（l）The pre-treatment of PEG/DMSO on donor cells significantly improved the fusion rate（51.11%vs 25.64%）（P＜0.05）；（2）Fusion rate in the fusion media containing O.lg/L polyvinyl alcohol（PVA）was higher than those in the media without PVA.Fusion rate in fusion media containing 0.32 mol/L mannitol（48.21%）was higher than those in the media with 0.28 mol/L，0.30 mol/L and 0.36 mol/L mannitol（27.78%，41.67%and 30.11%）；（3）Although the chamber is a much more routine way for fusing the reconstructed embryos，the tip shape electrodes can improve the fusion rate（42.31%，43.13%）comparing to routine parallel line electrodes（30.43%，33.33%）；（4）the efficiency of electrofusion of oocytes with fetal fibroblast cells at the found passage and the first passage was higher than that at the second and the third passage（38.98%，38.46%，36.73%and 35.00%），regardless of other fusion conditions.Conclusion Both the pre-treatment of PEG/DMSO on donor cells and the addition of PVA to the fusion media can improve the efficiency of electro fusion in the procedure of mouse SCNT.

Key words: PEG, Fusion, Mouse, Somatic cell nuclear transfer