Abstract: This study was designed to assess the effects of the sources of the donor cells and the treatments to the cells on the development of nucleartransferred embryos in vitro.Fibroblast cells of bovines were or not treated with serum starvation or preactivation,and then nuclei were gained.Reconstructed embryos (RE) were produced by microinjecting the nuclei into the cytoplasm of enucleated oocytes,of which the cleavage rate (CR) was checked at 24 and 36 h,and the blastocyst rate (BR) on D8.The experiment resulted in:1)There was no difference in CR and BR of RE among three aged (6,18 and 36 months) animals and two breeds (Angus and Holstein) for four individuals in total.2)CR of RE at 36 h,which produced with full-confluent fibroblast cells of 36-month Holstein experienced for 10-13 d serumstarvation duration,was lower than those for 0 d (control),3-5 d and 6-9 d;BR of RE was only lower than that for 3-5 d.3) CR and BR of RE,which produced from cells of 36-month Holstein,had no difference between the control and the preactivation by 5 μmol/L ionomycin or 7% ethanol.