Type 2 diabetes is an endocrine disease, which accounts for 9% of deaths worldwide. The aim of oral therapy is to reach normoglycemia to prevent later complications. Among glucose-lowering medications, alpha-glucosidase inhibitors delay the absorption of ingested carbohydrates, reducing the postprandial glucose and insulin peaks. In the present study, we tested the butanolic extracts of four Mexican plants with respect to their alpha-glucosidase inhibition activity, without excluding other possible mechanisms of action. The plants Cecropia obtusifolia Bertol., Equisetum myriochaetum Schlecht & Cham, Acosmium panamense (Benth.) Yacolev and Malmea depressa (Baill) R.E. Fries are used in traditional medicine to treat type 2 diabetes. In previous studies, we have demonstrated these plants' hypoglycemic activity and determined the phytochemical composition of their extracts. Our results in n-STZ diabetic rats loaded with maltose showed that Malmea and Acosmium extracts decreased plasma glucose significantly from 30 min on resembling the effect of acarbose. Cecropia extract produced the highest reduction of plasma glucose, and at 90 min, the glucose level was lower than the fasting level, which suggests another mechanism of action. Equisetum did not exert any effect. In vitro assays of alpha-glucosidase activity showed an IC(50) of 14 microg/ml for Cecropia, 21 microg/ml for Malmea, and 109 microg/ml for Acosmium, which were lower than that of acarbose (128 microg/ml). Equisetum did not show any significant effect on this assay, either. These results contribute to understand the mechanism of action of these plants on glucose metabolism.