A total of 152 mature female cattle was used in these experiments designed to develop an effective method inducing exact synchronization between the estrus cycles of donor and recipient cattle. All cattle, both donors and recipients, were treated with PMSG or PGF₂α on day 6 to 12 of the estrus cycle (day 0 = day of estrus). Donor cattle received a single injection of 2,750 to 3,500 IU PMSG, followed 48 and 60 hours later by the injection of 25 and 12.5㎎ PGF₂α, respectively. The estrus cycles of the recipient cattle were synchronized by single injection of 25㎎ PGF₂α 48 hours after the injection of PMSG to donor cattle. The results obtained in these experiments were summarized as follows: 1. Of 152 cattle treated with PGF₂α to induce synchronization between the estrus cycles of donors and recipients, 96.7% showed standing estrus, 1 to 4 days after initial PGF₂α administration. 2. The numbers of donor rattles showed standing estrus 1, 2 and 3 days after PGF₂α administration were 13(23.6%), 34(61.8%) and 6(10.9%), respectively. 3. The percentages of recipient cattle showed standing estrus 2, 3 and 4 days after PGF₂α administration were 24.7, 52.6 and 19.6%, respectively. 4. Sixty six percentages of recipient cattle were within the range of ±24 hours of exact synchronization of estrus with that of donor cattle which showed standing estrus at noon 2 days after PGF₂α administration.