[Objectives]  To investigate the adult activity and egg-hatching rhythm of Athetis dissimilis, a recently discovered pest in Chinese farmland, and provide a basis for the prediction and control of this species. [Methods]  The eclosion, feeding, mating, oviposition, and other behavioral rhythms of A. dissimilis were observed at (25 ± 1)℃, 70% ± 5% relative humidity, under a 14L︰10D photoperiod. [Results]  Eclosion of female and male A. dissimilis generally occurred during the photophase on the 12th day after pupation, with the respective peaks of each sex occurring from 13:00 to 17:00 and 13:00 to 15:00. Adults mainly fed on the first 2 days after pairing, and more adults fed during the scotophase (47.08%) than during the photophase (26.39%). Moreover, most adults mated on the 3rd day after pairing, with the peak of mating activity occurring from 03:00 to 07:00 in the scotophase. Mating duration ranged from 15 to 90 minutes, with an average of 47.33 minutes, with most (34.44%) pairs mating for between 30 and 45 minutes. The peak of oviposition occurred on the 5th day after pairing when 96.67% of females laid eggs, the majority of which were laid from 01:00 to 05:00 during the scotophase. Most (92.04%) eggs hatched on the 5th day after oviposition. The peak of hatching was from 17:00 to 23:00, during which the accumulated hatching rate was 64.99%, significantly higher than that at any other time period. Adult mobility peaked on the 2nd and 7th day after pairing, with 9.72% and 10.16% of adults moving, respectively. The proportion of mobile adults gradually increased during the scotophase, then decreased during the photophase. The proportion of adults of all ages observed resting during the photophase and scotophase was 83.67% and 64.94%, respectively. [Conclusion]  The eclosion, feeding, mating, oviposition, hatching, moving and resting behaviors of A. dissimilis have an obvious circadian rhythm, information that can aid the forecasting and control of this pest.