Previous studies by authors indicated that low temperature could result in more females of Schizothorax kozlovi during the early developmental stage. In order to elucidate the role of Cyp19b in sex differentiation of S. kozlovi, the full length cDNA of Cyp19b was cloned from the brain of S. kozlovi by using rapid amplification of cDNA ends (RACE) method. Relative mRNA expression levels of Cyp19b were determined by using quantitative real-time PCR (RT-PCR). Then the differences of Cyp19b mRNA expression levels in gills, brain, heart, liver, spleen, kidney, muscle, testis and ovary among different body-sized groups were discussed, while temperature effects on its expression during the larval stage of S. kozlovi were evaluated. The results indicated that: the full length cDNA of Cyp19b was 3 021 bp, which encoded 507 amino acids and belonged to brain aromatase gene; the deduced amino acid sequence of Cyp19b of S. kozlovi had more than 70% identity compared with brain aromatase genes of other teleost fishes, but only around 64% when compared with gonadal aromatase genes of other teleost fishes; the mRNA expression of Cyp19b of S. kozlovi only appeared in brain but not in other tissues, presenting relatively high tissue specificity; One-Way Analysis of Variance (ANOVA) revealed that the mRNA expression levels of Cyp19b were not significantly different between females and males in small body-sized samples (mean standard length was 12 cm), but gradually showed significant difference between females and males in large body-sized samples (mean standard length was 26 cm) (Fig. 3); larvae at 12 days after hatching were cultured in five different temperature groups, ANOVA revealed that six days later the mRNA expression levels of Cyp19b were significantly increased by low temperature (10℃ and 14℃), but not influenced by high temperature (26℃) (Fig. 4). The present results suggested that brain aromatase gene Cyp19b may play important roles in the feminization of S. kozlovi affected by low temperature during the early developmental stage.