To detect the sexual dimorphism pattern and its relationship between female fecundity in anuran, we caught 45 pairs of mating Duttaphrynus melanostictus individuals from Huangqiao Conservation Station in Wuyanling National Nature Reserve in March 2015, and measured their morphological traits [snout-vent length (SVL), head length (HL), head width (HW), interorbital space (IOS), tympanum diameter (TD), parotoid gland length (PGL), eye diameter (ED), length of lower arm and hand (LAHL), forelimb length (FLL), hindlimb length (HLL), body mass (BM)]. Then we collected female eggs to calculate their reproductive output (clutch mass and clutch size). We used linear regression to detect the relationship between morphological characteristics and SVL, the relationship between reproductive and body size, and the relationship of morphology within mating pairs. Paired t-tests were used to compare SVL and BM between sexes. One-way ANCOVAs were used to compare other morphological traits between sexes with SVL as covariate. We found female D. melanostictus had larger body size than males (Fig. 1, Table 1). Other morphological traits were positively correlated with SVL in both sexes (Fig. 2). Head length and hindlimb length were greater in males than in females after removing the effect of SVL, but other morphological characteristics did not differ significantly between sexes (Table 1). Both clutch size and clutch mass were positively related with female SVL and BM (Fig. 3), indicating that females could increase their fertility through increasing body size. Thus, in D. melanostictus, the formation of size sexual dimorphism was dominated by fecundity selection, while sexual dimorphism in other traits might be influenced by sexual selection and natural selection. Furthermore, we found only forelimb length showed significant correlation within paired toads (Fig. 4), which indicated there was assortative mating by forelimb length in D. melanostictus. In conclusion, current study provided direct evidence that fecundity selection could shape sexual dimorphism pattern in anuran, but also indicated that sexual selection and natural selection could influence the evolution of sexual dimorphism. Moreover, our results provided case study on assortative mating pattern in amphibians, and highlighted the importance of detecting multiple traits in assortative mating research.