Objective This study was performed to investigate the effect of hypoxia on glucose-6-phosphate isomerase (G6PI) expression and cell cycle of fibroblast-like synoviocytes from synovium of rheumatoid arthritis (RA) and osteoarthritis (OA) under hypoxia or normoxia.Methods Fibroblast-like synoviocytes were cultured with either of hypoxia (3％ oxygen) or normoxia (21％ oxygen) for 24 hours.The mRNA expression of G6PI and HIF-1α was tested by PCR quantification,while the protein levels of G6PI and HIF-1α were measured by western blot.Cell cycle was performed by FACS.T-test and Mann-Whitney U were used for statistical analysis.Results The expression levels of G6PI mRNA under hypoxia in RA were higher than those of OA (2.6±0.4 vs 1.5±0.4,P＜0.05).The protein levels of G6PI in RA were higher than those of OA (P＜0.05).The expression levels of HIF-1α mRNA under hypoxia in RA were higher than those of OA (2.9±0.8vs 1.4 ±0.4,P＜0.05).The protein levels of HIF-1α in RA were higher than those of OA (P＜0.05).The G1 phase ratio of cell cycle was decreased significantly under hypoxia than those of normoxia in RA ELs (t=1 1.31,P＜0.05).The S and G2 phase ratio of cell cycle were increased.Conclusion Hypoxia upregulates G6PI and HIF-1α expression and improves proliferation in fibroblast-like synoviocytes.