The red bigeye, Priacanthus macracanthus, is one of the major commercial fish species for trawl fisheries in southwestern Taiwan. In this study, its reproduction ecology was described based on 1,656 specimens collected between January 2011 and January 2012 caught by small trawlers. The sex ratio (% female) of 42.0% was significantly different from 50%, and among the females, those with a fork length greater than 240 mm were predominant. The relationship between body weight (BW) and fork length (FL) was estimated as BW=1.5×10-5FL3.026 (R2=0.936，n=1,656，p＜0.01) for the sex-combined data. Oocytes were mature when they attained a diameter of 0.5 mm or larger, and the eggs were transparent when they attained a diameter of 0.7 mm. The red bigeye fish reproduce once a year with an extended spawning season that lasts nearly year round. Specifically, the spawning period extended from January to July with a peak from February to April and July. The average fecundity of the species was 433,235 ± 278,533, with a mean batch fecundity of 91,763 ± 89,705. The ovarian egg maturation rate ranged from 0.9 to 54.6%, with an average maturation rate of approximately 14.8%, and the relative fecundity ranged from 115 to 6,190 (mean 2,187) per gram body weight. The relationship between the proportion of maturity (Pr) in each length interval and fork length was estimated to be Pr=1/(1+e16.39-0.076FL) (R2=0.98, n=695) for females and Pr=1/(1+e12.31-0.056FL) (R2=0.97, n=961) for males. The size at 50% of full maturity was estimated to be 214.6 mm FL for females and 219.8 mm FL for males. The 100% mature size was 290.0 mm FL for both males and females. The spawning ground of the red bigeye was located in the coastal waters from Kaohsiung to Tungkang and in the southeastern waters of Shiao-Liu-Chiu island at water depths of 100 to 150 meters. The waters of Tungkang, southwestern Shiao-Liu-Chiu island, and Fangshan were likely to be the nursery ground for red bigeye because the larvae were collected in these waters from March to July.