Objective To evaluate the efficacy and safety of azathioprine (AZA) in the treatment of refractory ulcerative colitis (UC).Methods Retrospective analysis of the clinical improvement,endoscopic improvement and mucosal healing rate,inflammation marker improvement after AZA administration and its safety in 24 refractory UC patients were performed,who were recruited between January 2007 and December 2011 in West China Hospital,Sichuan University,China.Results Twenty-four patients were enrolled,with a median age of 36 years old and a median course of 4 years.Among them,14 cases were moderate UC and 10 cases were severe UC.The patients were treated with AZA in a dose of (1.23 ±0.34) mg· kg-1 · d-1 from 7 weeks to 42 months.Efficacy was judged by Mayo disease activity index.At 3 months,6 months and 1 year after treatment,the effective rates were 73.9％ ( 17/23),81.8％(18/22) and 14/16 respectively,and the remission rates were 17.4％ (4/23),54.5％ (12/22) and 12/16respectively.Both ESR and C reactive protein level after treatment for 6 months and 1 year were significantly lower than those before treatment [ (9.3 ±8.9) mrn/1h,(10.9 ±7.3) mm/1h vs (22.3 ± 10.7) mm/1h;2.5(1.0-22.3) mg/L,2.3(1.0-28.0) mg/L vs 18.4(3.6-137.0) mg/L; all P ＜0.05].Corticosteroid withdrawal rates at 3 months and 1 year after AZA treatment were 16/18 and 15/16,respectively.At 6 months and 1 year after AZA treatment,the endoscopic improvement rates were 85.7％ ( 18/21 ) and 13/15 respectively; the cndoscopic remission rates were 61.9％ ( 13/21 ) and 11/15 respectively; and the mucosal healing rates were 61.9％ ( 13/21 ) and 11/15 respectively.Adverse effects were occurred in 8 patients.Leukopenia was the most common adverse effect,followed by liver function injury,alopecia and epigastric discomfort.Conclusions AZA is effective in the treatment of refractory UC patients with a low dose of ( 1.23 ± 0.34) mg· kg - 1 · d - 1,especially in the steroid withdrawing,maintaining remission and mucosal healing without severe adverse effects.