AIM: To investigate the characteristics and short-term efficacy of sulfasalazine (SASP) in patients with mildly and moderately active ulcerative colitis (UC).METHODS: Two hundred and twenty-eight patients with mildly and moderately active UC were recruited, 106patients in 1993-1995, and 122 patients in 2000-2002,they were assigned as the 1990s group (n = 106) and the 2000s group (n = 122), prospectively. The general characteristics, clinical manifestations, colonoscopic and histological data were compared between the two groups.The short-term efficacy and safety of SASP 3 g per d were evaluated.RESULTS: Between 2000s and 1990s groups, the gender ratio of men to women was 1:1.18 and 1:1.04, 57.4%and 50.9% of the patients were between 30 and 49 years old. The gender ratio and age of UC patients were not significantly different. The total course of 50.0% and 37.1% of UC patients was less than 1 year (P＜0.05), 10.6% and 31.2% of the cases had a duration of more than 5 years (P＜0.05) in 2000s and 1990s groups, respectively. The most common clinical type was first episode in 2000s group and chronic relapse in 1990s group. The patients showed a higher frequency of abdominal pain and tenderness in 1990s group than in 2000s group. Erosions were found in 84.4% and 67.9% of patients in 2000s and 1990s groups (P＜0.05). Rough and granular mucosa (67.9%vs43.4%, P＜0.05)and polyps (47.2% vs 32.8%, P＜0.05)were identified in 1990s group more than in 2000s group.There were no significant differences in clinical, colonoscopic and histological classifications. After SASP (1 g thrice per d) treatment for 6 wk, the clinical, colonoscopic and histological remission rates were 71.8%, 21.8% and 16.4%,respectively. In 79 patients with clinical remission, 58.2%and 67.1% remained grade 1 in colonoscopic and histological findings, respectively. The overall effects in first episode type (complete remission in 10, 18.9%, partial remission in 28, 52.8%, and improvement in 9, 17.0%) were better than in chronic relapse type (complete remission in 3,7.5%; partial remission in 16, 40.0%; and improvement in 15, 37.5%) and chronic persistent type (complete remission in 1, 5.9%; partial remission in 6, 35.3%; and improvement in 6, 35.3%) respectively (P＜0.05). In 110patients treated with SASP, 18 patients (16.4%) had adverse reactions. Except for two cases of urticaria and one case of WBC decrease, none of the patients had to stop the treatment because of severe adverse reactions.CONCLUSION: Patients with mildly and moderately active UC in 2000s group had a shorter disease course, milder clinical manifestations, more first episode type and higher frequency of acute mucosal lesions in colonoscopy than in 1990s group. The patients in 1990s group had higher proportion of chronic relapse type and chronic mucosal change in colonoscopy than in 2000s group. The shortterm efficacy of SASP could be mainly remission of clinical manifestations. But more than half of the patients still had light inflammation in colonoscopy and histology. The overall effects of SASP in first episode type were better than those in other types. SASP was a safe and effective drug to treat mildly and moderately active UC.