Abstract:The inhibitive effects in vitro of Dictyota dichotoma polysaccharides on α-glucosidase activity was studied.The polysaccharide from Dictyota dichotoma was extracted by ultrasonic-assisted technology，ethanol precipitation，deproteinization，decolorization and desiccation.Using p-nitrophenyl-α-D-glucopyranoside（PNPG）as the substrate，the enzyme-inhibitor model was used to study the inhibition ability of polysaccharide from Dictyota dichotoma of the α-glucosidase and the double reciprocal plot method was used to determine the type of inhibition.The inhibitory effect of Dictyota dichotoma polysaccharides was impacted by pH，temperature，time and polysaccharide concentration.The optimal pH，temperature，reaction time and concentration for Dictyota dichotoma polysaccharides inhibitory effect on α-glucosidase were pH 6.8，37 ℃，20 min，respectively.The half -maximal inhibitory concentration （IC50） value of Dictyota dichotoma polysaccharide was 22.64 mg/mL，showing a good hypoglycemic function.The inhibition type was mixed inhibition.The enzyme-inhibitor model showed that the polysaccharide from the Dictyota dichotoma had a certain inhibition effect on the activity of α-glucosidase．