Rheumatoid arthritis (RA) is a disease with significant gender differences in its prevalence and clinical features. Interleukin (IL)-1 and tumor necrosis factor (TNF) α produced by synoviocytes are principle inflammatory and destructive mediators of RA. We found that a potent androgen, 5α-dihydrotestosterone (DHT) inhibits IL-1α-induced production and mRNA expression of IL-8, IL-6 and IL-1β from RA patient-derived fibroblast-like synovial cell line MH7A. Promoter analysis of the IL-8 gene revealed that nuclear factor (NF)-κB activation is critical for its transcriptional activation by IL-1α, and DHT inhibited the IL-1α-induced NF-κB activation in a manner dependent on the androgen receptor (AR). DHT also inhibited the effects of TNFα on the cells overexpressed with AR, indicating that sufficient expression level of functional AR was necessary for the inhibitory effect of DHT on TNFα. These results suggest that androgen contributes to the prevention against RA and its gender difference by inhibiting IL-1α or TNFα-induced proinflammatory cytokine production from synovial fibroblast-like cells by inhibiting NF-κB activation in a manner depending on AR.