Alfalfa is considered nutritious and beneficial for human health, but it is widely used as animal feed. To develop alfalfa functional food, this study investigated the physical, functional and structural properties of alfalfa leaf powder with particle sizes ranging from 0.063–0.250 mm. The brightness, solubility, and enzyme inhibitory activity of alfalfa leaf powder increased, as the particle size of powder decreased from 0.200-0.250 mm to 0.063-0.08 mm. The angle of repose, compressibility, transition temperature, and melting temperature were the lowest (41.37°, 15.63%, 79.00℃, and 160.54℃ respectively), the swelling index was the highest (4.39 mL g-1), when the particle size of powder ranged from 0.125–0.160 mm. Further analysis of the microstructure showed that the surface roughness, the number of hydroxyls and the crystallinity index decreasing, as the particle size of powder decreased from 0.200-0.250 mm to 0.063-0.08 mm. Results showed that the particle size of alfalfa leaf powder ranging from 0.125–0.160 mm is more convenient to process and prevent obesity, smaller size is more beneficial to prevent hypertension and aging.