Objective: To optimize preparation process of casticin chitosan microspheres and investigate its in vitro release characteristics. Method: Casticin chitosan microspheres were achieved by emulsion crosslinking method

taking liquid paraffin as oil phase

span-80 and tween-80 as emulsifier

and glutaraldehyde as crossinking agent.Design-Expert 8.0.6 software was applied to optimize preparation procedure.Morphology of the microspheres was observed by scanning electron microscope (SEM).Dynamic dialysis method was used to determine in vitro release characteristic of casticin chitosan microspheres. Result: Optimum preparation process of microspheres was as following:ratio of oil phase to water phase of 6:1

crosslinking time of 3 h

rotation rate of 1 400 r·min-1.Casticin chitosan microspheres had rounded shape and uniform particle size distribution

its average diameter was 7.92 μm

drug-loading was 29.20%and encapsulation efficiency was 39.23%.Release behavior of casticin chitosan microspheres was described by Higuchi model in phosphate buffer solution with pH of 7.4.Cumulative release amounts of casticin chitosan microspheres in 4 h and 48 h were 26.75%and 95%

respectively. Conclusion: This optimized preparation process is feasible and simple

casticin chitosan microspheres has high drug-loading with a sustained-release effect.