Interleukin-23 (IL-23) is a novel pro-inflammatory cytokine which has been implicated to play a pathogenic role in rheumatoid arthritis (RA). This study was undertaken to investigate the IL-23 inductive activity of the proinflammatory cytokine IL-17, IL-1β and tumor necrosis factor (TNF-α) in RA synovial fluid mononuclear cells (SFMC). Expression of IL-23p19, IL-17, IL-1β and TNF-α in joint was examined by immunohistochemistry (IHC) of patients with RA and osteoarthritis (OA). The effects of IL-17 and IL-1β on expression of IL-23p19 in human SFMC from RA patients were determined by reverse transcriptase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). IL-23p19 was expressed in the RA fibroblast like synoviocyte (FLS), but not from OA FLS. Similar to the protein expression, IL-23p19 mRNA could be detected by RT-PCR in RA SFMC. IL-17 and IL-1β could induce RA SFMC to produce the IL-23p19. The effects of IL-17 were much stronger than IL-1β or TNF-α. These responses were observed in a dose-responsive manner. In addition, IL-17 or IL-1β neutralizing antibody down-regulated the expression of IL-23p19 induced by LPS in RA-SFMC. Our results demonstrate that IL-23p19 is overexpressed in RA synovium and IL-17 and IL-1β appears to upregulate the expression of IL-23p19 in RA-SFMC.