The objective of this study was to investigate the relationship between various estrous behavior and ovulation time, and to determine which estrous behavior could predict ovulation time more accurately. In total, 37 ovulations and 28 estrous detection were observed in 51 Holstein-Friesian dairy cows. Various estrous behavior were observed during 72 h from two days after $PGF_2{alpha}$ injection and their relation with the time of ovulation (ultrasound examinations at 4-h intervals) was investigated. In estrous periods, the rate of sniffing, chin resting, mounting, standing heat was 81%, 78%, 78% and 56%, respectively. Ovulation occurred $25.6{pm}7.9h$ after onset of estrus (ranging between 7 and 37h) and $13.4{pm}7.1h$ after end of estrus (ranging between 1 and 28h). Interval between onset of estrus and ovulation time was significantly (p<0.05) shorter for standing heat $(17.33{pm}5.83h)$ than for mounting, sniffing and chin resting $(23.58{pm}5.12h,;24.25{pm}6.09h,;23.42{pm}6.04h)$. In 88% of the animals that displayed mounting, ovulation occurred between $16{sim}28h$ after onset of mounting. Onset of standing heat, sniffing and chin resting occurred between $10{sim}22(81%)h,;16{sim}28(79%)h;and; 19{sim}31(79%)h$ before ovulation respectively. Sniffing and chin resting were displayed during the non-estrous period and are therefore, not useful predictors of ovulation time. The standing heat and mounting can be a good predictor for time of ovulation but the disadvantage of using standing heat is that only a limited number of cows display standing heat. Thus, it is concluded that mounting behavior could be the best predictor for time of ovulation.