In view of alleged antidiabetic potential effect of the methanol, n-hexan and dichloromethane extracts of Equisetum arvense of blood sugar and body weight in streptozotocin-induced (50 mg kg(-1), i.p. dissolved in normal saline) diabetic rats were investigated. The blood glucose lowering activity of the methanol, n-hexan and dichloromethane extracts was determined in steptozotocin-induced diabetic rats; after oral administration in doses of 50, 100, 250 and 500 mg kg(-1) daily for 5 weeks. The data was compare statistically using one-way ANOVA tukey test. The results showed that in different doses of methanolic extract, dichloromethane extract at doses of 50 and 250 mg kg(-1) and n-hexan extract (50 mg kg(-1)), blood sugar decreased significantly in comparison with the treatment and control groups of diabetic rats. Also the weights of methanolic-extract treatment group were higher than the other treatment groups. The present studies clearly indicate a significant antidiabetic effect with the methanolic extract of Equisetum arvense and lend support for its traditional usage. Further investigation on identification of the active principles and their mode of action are needed to unravel the molecular mechanisms involved in the observed effects.