Abstract: OBJECTIVE To prepare Hawthorn leaves flavonoids sustained release capsules and investigate the release mechanism. METHODS Hawthorn leaves flavonoids sustained release solid dispersion was prepared by spray drying method, using ethyl cellulose as carrier, with 2, 6 and 12 h of the cumulative release amount as index, to determine the best sustained release solid dispersion prescription. X-ray diffraction, scanningelectron microscopy and infrared spectroscopy were used to investigate the drug dispersionin state in the solid dispersion. Kawakita equation was fitted with the fluidity of the powder parameters as index to screen the prescriptions, prepare the Hawthorn leaves flavonoids sustained release capsules, investigate the release mechanism of the capsules and fit the release kinetics equation. RESULTS The best prescription of Hawthorn leaves flavonoids sustained release solid dispersion composition:Hawthorn leaves flavonoids:ethyl cellulose:carbopol=4:1:0.5; XRD and SEM results showed that the drug in amorphous form or molecular form dispersed in the sustained release solid dispersion. Infrared spectroscopy results showed that no interactions were between Hawthorn leaves flavonoids, ethyl cellulose and carbomer. The optimal sustained release capsules prescription was solid dispersion:silica gel as 1:0.3%. The sustained-release capsules by accumulative release percentage of 2 h was 27.56%, 6 h was 69.50%, 12 h was 96.78%. CONCLUSION The sustained-release capsules show good sustained release characteristics in 12 h. The release behavior conforms to the first-order kinetic equation, the release mechanism is the combination of diffusion and erosion, and the degradation of controlled release type.