AIM: To investigate the short-term efficacy and safety of sulfasalazine (SASP) 3 g per day in the treatment of patients with mild and moderate ulcerative colitis (UC). METHODS: 122 patients were treated with SASP ( 1 g, t.i.d.) for 6 weeks. The data of clinical manifestations, colonoscopic and histological involvements were compared before and after the treatment of UC. The short-period efficacy and adverse reactions were evaluated in 110 patients. RESULTS: The therapeutic project was carried out in the 110 out of 122 patients. After 110 patients were treated for 6 weeks, the clinical, colonoscopic and histological remission were 71.8%, 21.8% and 16.4%, respectively. Among the 79 patients with clinical remission, 58.2% and 67.1% of them remained grade 1 in colonoscopic and histological findings, respectively. The curative rates and the effective rates were 63.9% and 82.0%, respectively. Among the 122 patients treated with SASP, 21 of them ( 17.2%) had adverse reactions. Except 4 patients suffered urticaria and leukopenia, no patients quitted the treatment because of obvious adverse reaction. CONCLUSION: SASP ( 3 g per day) can be an effective and safe medicine in treatment of patients with mild and moderate UC, but more than half of the patients in clinical remission still have light inflammation in colonoscopy and histology.