Abstract: Objective To determine the correlation between in vitro release and in vivo absorption of sustained-releasing tablets of neostigmine bromide. Methods Water was used as dissolution medium to measured in vitro release of neostigmine bromide. After a single oral administration of 100 mg neostigmine bromide to rabbits, the plasma concentrations of neostigmine bromide in the rabbits were determined by HPLC. The compartment model and deconvolution method were employed to explain the in vitro-in vivo correlation. Results Using Y as cumulative in vitro release and Fa as percentage of absorption, the regression equation was established:Fa=0.9298Y+4.6074,r=0.9961. The input function of R=2.0163Y-11.242,r=0.9270. Conclusion The correlation between in vitro release and in vivo absorption of neostigmine bromide is good.