The reproductive biology of Octocoral (Plumarella flabellata) in artificial habitats located in Northwest of Persian Gulf, Iran was studied by histological examination of gonad development. Various sizes of colonies were collected to determine the relationship between colony size and sexual maturity. The colonies smaller than 15 cm height did not contain gonads. Moreover, P. flabellata was a hermaphrodite species with gonads developed along with mesenteries. No planulae were observed in the samples investigated. Therefore, P. flabellata in Iran is most likely a broadcast spawener. The gonads were at the same developmental stages in each season. The results showed that spawning of P. flabellata probably occurred in July-August which is consistent with the suitable environmental conditions such as higher water temperature and long day-light. The present study indicated that P. flabellata exhibits a remarkably high reproductive potential, which contributes to its dominance in the artificial reef in Northwest of Persian Gulf.