The objective of this study was to investigate the efficiency of estrus detection and determination of the time of ovulation in Japanese Black cows by a real-time radiotelemetric pedometer. A herd of Japanese Black cows was housed in a loose-housing barn. This pedometer system and a pressure-sensing radiotelemetric device, which detects standing events, were concurrently compared in regard to their availability for detection of estrus events. Pedometer estrus and standing events were observed for all cows (n=20), and the duration of increased walking activity was 15.8 ± 0.9 h, which was longer (P<0.0001) than the duration of standing events (9.0 ± 1.3 h). Ovulation was observed 30.2 ± 0.6 h after the onset of pedometer estrus and 29.0 ± 0.6 h after the first standing event. There was a high correlation (r=0.89, P<0.0001) between the intervals from the onset of pedometer estrus and onset of standing event to ovulation. The animals of the pedometric group (n=20) were inseminated 10 to 18 h after the onset of pedometer estrus and had a higher conception rate (90.0%, P<0.05) than those inseminated according to the a.m. /p.m. method (58.4%, n=24). In conclusion, the pedometer system is an excellent tool for precise estrus detection and insemination at the appropriate time, which ensure a high pregnancy rate in Japanese Black cows.