Aqueous extracts of medicinal plants Nigella sativa, Eugenia jambolana and Andrographis paniculata, Gymnema sylvestre were prepared by maceration. They were then tested for inhibition of α-amylase activity by DNSA colour reagent. They were tested for their ability to hinder diffusion of glucose across a dialysis membrane. The aqueous extract of Nigella sativa showed maximum inhibition of α-amylase activity and a strong hindrance to diffusion of glucose across a dialysis membrane. Andrographis paniculata showed both a strong inhibition of α-amylase and a significant hindrance to the diffusion of glucose across the dialysis membrane. Gymnema sylvestre showed low inhibition of α-amylase activity but it showed maximum hindrance to the diffusion of glucose across the dialysis membrane. Nigella sativa was found to possess maximum anti-diabetic properties. All the above plants possess anti-diabetic properties to varying degrees. They can be used to develop natural drugs which may be used in lieu of commonly used strong allopathic drugs which possess a number of harmful side effects.