Abstract: To optimize the decolorization process of alkaloids from mulberry leaf by activated carbon and effect of decolorization treatment on its α-glucosidase inhibition activity, alkaloid extract of mulberry leaf was taken as the research object. The decolorization rate and retention rate were normalized to Z value by weighted scoring method. The effects of four factors on the decolorization effect of activated carbon were investigated by single factor and L₉ (3⁴) orthogonal test to optimize the decolorization process. The inhibition rate of decolorized and non-decolorized alkaloids on the activity of α-glucosidase was determined through in vitro experiment. The results showed that, the optimum decolorization conditions were screened as follows:The alkaloids extract of mulberry leaf was decolorized twice by 4% activated carbon at 60℃ for 25 min, and the decolorization rate and retention rate were 79.80% and 78.52%, respectively, and the Z value was 100. The inhibition rate of decolorized alkaloids with the concentration of 2.0~8.0 mg/mL on the α-glucosidase inhibitory activity was significantly higher than that of non-decolorized (P<0.05). The maximum inhibitory rate of the alkaloids from mulberry leaf was 51.37% and 63.06%, respectively. And the IC₅₀ concentration of decolorized and non-decolorized alkaloids were 4.27 and 7.75 mg/mL, respectively. The decolorization process of alkaloids from mulberry leaf by activated carbon is established in this paper, and the α-glucosidase inhibitory activity of decolorized alkaloids is stronger than that of non-decolorized, which provides an experimental basis for extraction and purification of alkaloids from mulberry leaf.