Abstract: The aim of the present study was to test Diamicron`s effectiveness in a group of Iranian patients. In a clinical trial study, 40 diabetic patients which their hyperglycemia was not controlled with diet and exercise were enrolled to take Diamicron MR for a 12 weeks period and their Fasting Plasma Glucose (FPG) and HbA1c measured during treatment. Data were analyzed by SPSS11 statistical package. Repeated measures ANOVA and Paired t tests were used to analyze data . Twenty four persons (60%) were males and 16 of them (40%) were females. The mean for age was 48.8±13.2 (SD) years. FPG in patients before starting drug treatment had a mean of 236.65±75 mg dL-1. Mean of FPG for second week after start of treatment was 180±65 mg dL-1. It was 152±61 mg dL-1 on 4th week and 136±35 mg dL-1 on 8th week. Mean of FPG on 12th weeks was 131±40 mg dL-1. HbA1c was checked both at the beginning of treatment and at the 12th week. Its mean was 11.1±1.9 at the beginning and it was 8.6±1.6 after 12 weeks. The decrease in FPG and HbA1c during the treatment period compared to pretreatment FPG was statistically significant (p<0.01). Diamicron MR was effective in controlling hyperglycemia with a good compliance and less complications in Iranian patients.