In this study, three cDNA sequences corresponding to cytochrome P450C17 (CYP17 I), 3β-hydroxysteroid dehydrogenase (3β-HSD) and androgen receptor (AR) were isolated from spotted sea bass ( Lateolabrax maculatus). The mRNA abundances of CYP17 I and 3β-HSD increased from stage Ⅱ to stage Ⅴ with a significant increase at stage Ⅴ, and the highest abundance of AR mRNA was detected at stage Ⅲ in testicular development cycle. CYP17 I, 3β-HSD and AR transcripts were obviously abundant in steroidogenesis tissues such as testis, brain, head kidney among others. Strong and positive signals were observed mainly in interstitial cell regions of L. maculatus testis as were measured with in situ hybridization method. Significant increases of CYP17 I and 3β-HSD transcripts were detected after 12– 48 h hCG (human chorionic gonadotropin) and GnRHa (gonadotropin-releasing hormone analogue) treatments. However, an opposite relationship was found for AR in testis at the same time. In addition, decreasing trends of CYP17 I and 3β-HSD mRNA were observed in testis of L. maculatus in freshwater group (FW) from day 2 to day 6, and mRNA abundance of AR increased in brackish water (BW) group from day 4 to day 8. These findings revealed that these three steroid synthesis genes are import for testicular development, hormone and salinity treatment, and provided also an insight into the mechanism of reproductive endocrine of L. maculatus.