The ovarian cycle, the biological minimum size, and artificial spawning frequency by artificial spawninginduction of the female hard clam, Meretrix petechialis, were investigated by histological observations and morphometricdata. The ovarian cycle of this species can be classified into five successive stages: early active stage, late active stage,ripe stage, partially spawned stage, and spent/inactive stage. The spawning period was from June to September, and themain spawning occurred between July and August when the seawater temperature exceeds over 20℃. The biologicalminimum size (shell length at 50% of first sexual maturity) in females were 40.39 mm in shell length (considered to betwo years of age), and all clams over 50.1 mm in shell length sexually matured. In this study, the mean number of thespawned eggs by spawning induction increased with the increase of size (shell length) classes. In case of artificial spawninginduction for the clams > 40.39 mm, the number of spawned eggs from the clams of a sized class was gradually decreasedwith the increase of the number of the spawning frequencies (the first, second, and third spawning). In the experimentsof artificial spawning induction during the spawning season, the interval of each spawning of this species was estimatedto be 15-18 days (approximately 17 days).