[Objectives]  To investigate the mating rhythm of Protaetia brevitarsis, an important agricultural and forestry pest, in order to improve the monitoring, prediction and control of this species. [Methods]  Mating behaviors of P. brevitarsis adults of different ages were observed at (23 ± 1) ℃, 60% ± 5% relative humidity, under a 14L : 10D photoperiod. [Results]  The mating behavior of P. brevitarsis can be divided into four stages; courtship, mounting, copulation and post-copulatory guarding. No courtship behavior was observed in 1-5 day-old adults. Courtship and copulation occurred in adults over 10 days of age, and peaked in those 30-35 days of age. Significantly fewer 10-15-day-old adults engaged in courtship than those aged 20-25, 30-35, or 40-45 day-old. The mating rate of 30-35 and 40-45 day-old adults was significantly higher than that of those 10-15 and 20-25 days old. Moreover, mating mostly occurred from 11:00-14:00; no mating behavior was observed at night. The duration of copulation ranged from 1 to 12 min, with an average of 7.47 min. 53.85% of observed copulation lasted for 6-9 min. [Conclusion]  The results indicate that the mating behavior of P. brevitarsis adults has an obvious circadian rhythm, and that supplemental feeding has no significant effect on mating success.