This multicenter clinical trial was performed to evaluate the efficacy and safety of mizoribine for the treatment of Sjögren's syndrome. Fifty-nine patients with a definite diagnosis of Sjögren's syndrome received 150;Smg of mizoribine daily for 16 weeks. The salivary secretion volume was determined at baseline, at weeks 8 and 16 after the start of the study treatment by the Saxon test, and clinical manifestations were assessed by the investigator and the patients using a 10-cm visual analog scale (VAS). Adverse drug reactions were reported in 18 patients, of whom 6 patients had to discontinue the study due to such adverse reactions; however, no serious adverse drug reactions definitely related to the study drug were noted. The salivary secretion volume, the rate of change in salivary secretion, the patients' own assessments of dry mouth and dry eyes, the investigators' assessment of oral sicca symptoms, and the investigators' overall assessment improved following the treatment regimen with statistical significance at week 16 after the start of treatment in comparison to the baseline values. These results suggested that mizoribine may be effective in producing a subjective and objective amelioration of the glandular symptoms in patients with Sjögren's syndrome, without observing any serious adverse effects related to this drug.