The reproductive characteristics such as reproductive cycle, gonad maturation, gonado-somatic indices (GSI) and fecundity of 639 kingsoldier bream, Argyrops spinifer , a commercial species of Sparidae family in the Persian Gulf were investigated by monthly sampling during June 2010 to May 2011. Samples were caught by local fisherman using trawl net in waters of Bushehr province in the northern part of the Persian Gulf. Each month, a total of 50 to 60 specimens of fish were examined, on average. Total length of fish sampled ranged from 15 to 61.2 cm in males and 13.5 to 64.2 cm in females and total weight ranged 77-3450 g and 52.5-4162 g in males and females, respectively. Size (Lm 50 ) and age (Am 50 ) at first maturity were estimated to be 30.1 cm total length and 5 years for males and 31.3 cm total length and 6 years for females, this indicate that A. spinifer is exploited below the mean size at sexual maturity. Age determination using annual growth rings on sagittal otoliths was estimated. Age groups of females and males were in the range of 2 + to 21 + and 2 + to 25 + , respectively. The overall sex ratio was 0.8:1 (male: female) and were significantly different from the expected ratio of 1 : 1 (p 0.05, ? 2 test). The most frequent age groups were 2 + and 3 + in males and females, respectively. The highest value of condition factor was observed in January for females and in February for males. The minimum, maximum and average absolute fecundity were 79061, 2374796 and 682940 ± 527998, respectively for females 17-47 cm total length and weighing 117.5-1666 gr. The relationship between absolute fecundity and fish total length was represented by the following linear equation: F= 54417 L – 92699 (r = 0.767), and a linear equation: F = 1165 W + 41595 (r = 0.806) was found between absolute fecundity and fish weight. The analysis of ova diameter for the species revealed that there are 3 egg batches in ripe ovary of A. spinifer and swing diameter of eggs in the ovaries of these fish throughout the year, was between 25 to 800 microns. Regarding gonado-somatic index (GSI) values, oocyte diameter, histological studies and abundance of different stages of maturity at different month, it seems that spawning of A. spinifer occurs from December to April. Indeed, gonad maturation started from December and spawning completed in March and April. Long spawning season suggests that A. spinifer is a multiple spawner with an asynchronous ovary. This finding could be confirmed by oocyte diameter and histological studies, too. No changes in gonad conditions were noted from May to October. The results of the present study presume state of both protogyny and rudimentary hermaphroditism in A. spinifer . The results of this study provide fundamental information on the reproduction biology of A. spinifer in the Northern Persian Gulf that can be used in management models for the continued sustainable exploitation of this species in the Iranian demersal coastal fisheries. Keywords : Kingsoldier bream, Argyrops spinifer , Sparidae, Persian Gulf, Reproductive characteristics.