The brushtooth lizardfish, Saurida undosquamis, is one of the important commercial species for the trawl fishery in southwestern Taiwan. Its reproductive biology was described based on 2,078 specimens collected between May 2008 and May 2009 caught by small trawlers in the waters off southwestern Taiwan. The sex ratio, 51.3% (1,065/2,078), was significantly different from 50%, and females predominated for fork length greater than 350 mm. The sexes-combined relationship between body weight (BW) and fork length (FL) was estimated as BW = 6.0 × 10-6 × FL3.091 (R2 = 0.974, n = 2,078, χ2=0.001, p<0.05). Oocytes were mature when they attained 0.5 mm or larger in diameter, and the transparent oocytes were found when their diameter attained 1.00 mm. A multiple spawning pattern was observed for this species, and its spawning season extended from September to May and peaked from February to April based on the microscopic observation, gonadosomatic index, condition factor, oocyte diameter monthly distributions and hepatosomatic index. The mean fecundity was estimated to be 168,373 ± 132,060. The mean batch fecundity was estimated to be 29,200 ± 26,978, and relative fecundity ranged from 100 ~ 2,087 (mean 890) per gram of body weight. The mature rate of ovarian eggs ranged from 3.4% to 29.2%, with an average of 15.9%. The logistic curves describing the relationship between proportion of maturity (Pr) in each length interval and fork length were estimated to be Pr = 1/ (1+e7.60-0.0386FL) (R2 = 0.861) for females and Pr = 1 / (1+e4.85-0.0239FL) (R2 = 0.914) for males. Sizes at 50% maturity were estimated to be 196.8 mm and 202.6 mm FL and at 100% maturity were estimated to be 425.0 mm and 375.0 mm FL for both females and males, respectively.