Abstract: AimTo investigate the effect of preparation technique on In vitro release mechanism of huperzine A -PLGA microspheres. MethodsHuperzine A -PLGA microspheres were prepared by two kinds of O/O emulsion solvent evaporation method (method A and B). In vitro release mechanism was explained by release profile, degradation rate and swelling rate of microspheres In vitro. The microspheres morphology and drug distribution within microspheres were observed in order to explain further the drug release mechanism. ResultsThe encapsulation efficiency of huperzine A microspheres prepared by method A and B was 47.60% and 83.50% respectively. Microspheres prepared by method A could sustain release for 35 days with nearly no initial burst release. The release profile fitted well to zero order equation and drug release mainly through degradation and diffusion mechanism. Huperzine A microspheres prepared by method B could sustain release for 21 days with some evidence of initial burst release. The release profile fitted well to the Higuchi equation and drug release was mainly through diffusion mechanism. ConclusionHuperzine A microspheres prepared by method A had more desirable release profile.