To establish the method of estrus induction using the injection of PGF$_2$$alpha$ㆍ the 60 dairy cows treated by PGF$_2$$alpha$ㆍ at 6, 8, 10, 12, 14, and 16 day of estrous cycle, recpectively. The plasma progesterone concentrations at day of injection of PGF$_2$$alpha$ㆍ were $1.5pm$1.3 (mean$pm$SD) ng/ml at 6 days of estrous cycle, 3.7$pm$1.4 ng/ml at 8 days, 6.5$pm$1.8 ng/ml at 10 days, 7.9$pm$2.0 ng/ml at 12 days, 6.5$pm$2.5 ng/ml at 14 days, and 2.5$pm$1.2 ng/m] at 16 days, respectively. The percentages of induction of estrus after PGF$_2$$alpha$ㆍ treatment were 52.8% at 3th day after treatment, 21.7% at 4th day, 8.3% within 2th day, and ] 7.2% after 5th day, respectively. The percentages of cows conceived at first service after induction of estrus were 73.3% on 16 days of estrous cycle at treatment, 66.7% on 10 and 14 days, 63.3% on 8 and 12 days, and 53.3% on 6 day, respectively. The percentages of cows conceived on first service were 70.5% at 3th day after induction, 66.7% at 4th day and 65% at 5th day, respectively. These results suggest that the PGF$_2$$alpha$ㆍ treatment at regressing stage of corpus luteum showed high induction of estrus and pregnancy rate, and there were high induction of estrus and pregnancy rate at 3th and 4th day after PGF$_2$$alpha$ㆍ treatment.