Objective: To investigate ultrafine grinding rules of Angelicae Dahuricae Radix pieces. Method: Fine powder and ultrafine powder Ⅰ

Ⅱ

Ⅲ

Ⅳ of Angelicae Dahuricae Radix were prepared

size distribution

wettability

infrared spectrum and moisture absorption were used to evaluate these powders.HPLC was employed to determine the content of imperatorin and evaluate dissolution with methanol-water(70: 30) as mobile phase and detection wavelength at 251 nm. Result: Particle size of ordinary powder was the maximum and ultrafine powder Ⅳ was the minimum.Wettability of ordinary powder was the worst

but it improved significantly after being ultrafine ground.Wettability of ultrafine powder Ⅳ was the best and its contact angle approached zero.Infrared spectrum and moisture absorption of these five kinds of powders were extremely similar

dissolution of ultrafine powder Ⅲ was better than others. Conclusion: Chemical compositions in four kinds of ultrafine powders do not change by comparing with ordinary powder

while their micromeritic properties are difference

it shows that ultrafine grinding of herbs should choose appropriate particle size acorrding to specific application.