This study was carried out to monitor the response of ovaries and cyst according to treatment with dinoprost or fenprostalene in dairy cows with ovarian luteal cyst. Twenty cows were diagnosed as luteal cysts by rectal palpation, ultrasonography and progesterone analysis. The cystic cows were treated with dinoprost or fenprostalene. All the animals were re-examined by ultrasonography and blood was collected for the measurement of plasma progesterone concentration at day 0 (the day of treatment), 3, 13 and 24, respectively. Mean plasma progesterone concentrations on day -11 and day -1 before treatment were 2.1$pm$0.2 ng/ml and 2.8$pm$0.3 ng/ml, respectively. On day 3 and day 13 were 0.3$pm$0.1 ng/ml and 4.3$pm$0.2 ng/ml, respectively. Mean cystic wall thickness on day -11 and day -1 were 3.2$pm$0.2 mm and 3.9$pm$0.2 mm, respectively. And on day 3 was 2.4$pm$0.3 mm. The responses of luteal cyst after treatment noted during ultrasonography included dramatical degeneration of the luteal tissue of cystic wall on day 3 (all cows), slowly reduction of cyst size (cyst resolution) until last examination (8 cows), complete disappearance on day 13 (7 cows) and no changes of cyst size (5 cows). A group of 10 cows with luteal cysts injected fenprostalene compared with another 10 cows treated dinoprost showed a slightly higher pregnancy rate on first service after initial treatment (50.0 vs 30.0%). But treatment effects of dinoprost or fenprostalene did not significantly different results for each groups. This study suggested that the response of the cyst according to treatment revealed various types. Therefore, veterinarians should have attention on monitoring of the response of cystic ovaries after treatment, specially on no change of cyst size after treatment.