Abstract: OBJECTIVE Study on the influence of different grain sizes on the dissolution of the ferulic acid and other chemical composition. METHODS Ultra-fine, 40 mesh and 100 mesh powder of the Angelica Sinensis Radix were quantitatively and qualitatively studied by HPLC. RESULTS Comparing with 40 mesh and 100 mesh powder of Angelica Sinensis Radix treated with sonication for 10 min, the ferulic acid-soluble out rate of the ultra-fine powder were increased separately by 82.5% and 81.09%. Furthermore, the number of peaks in the HPLC graph of ultra-fine powder was more than that of 40 mesh and 100 mesh powder, which indicated that more chemicals in the Angelica Sinensis Radix were dissolved out. And also, the area of relative peaks of ultra-fine powder were larger than that of the traditional ones. CONCLUSION The technique of ultra-fine grinding can significantly improve the dissolution of the chemical constituents of Angelica Sinensis Radix.