Eucommia ulmoides leaves (EUL) are a potential alternative to E. ulmoides bark in traditional Chinese medicine owing to their similar chemical constituents and biological effects. To investigate the impact of grinding on the physicochemical properties, active ingredients, and in vitro activities of EUL, three raw materials with different particle sizes were prepared using coarse grinding and superfine grinding techniques, namely, coarse grinding powder (CG), 100-mesh powder (M100), and superfine grinding powder (SG). The physicochemical properties, polysaccharide content, in vitro hypoglycemic activity, and antioxidant activity of EUL were then examined. The results showed that SG had the smallest particle size (D50=9.63 μm) and the highest bulk density, tapped density, water-holding capacity, oil-holding capacity, and solubility; however, its flowability was poor. The polysaccharide content in SG was 22.47%, while the inhibition rates of its polysaccharides on α-glucosidase and α-amylase, and its scavenging rates for DPPH•, O2-•, and •OH, were significantly superior to those of other samples. In conclusion, superfine grinding effectively improved the physicochemical properties of EUL powder and enhanced its in vitro hypoglycemic and antioxidant activities. Hence, this technique can be employed as a beneficial pretreatment for large-scale production of EUL in the food and pharmaceutical industries. Additionally, SG can also serve as a usable raw material for functional foods and nutritional supplements.