Abstract: Insulin/montmorillonite (INS/MMT) complexes were prepared by purified Na-montmorillonite and insulin under a certain condition. The absorption ability of Na-montmorillonite was analysed, and the effects of pH and time on INS release from the complexes were explored. Three models of in vitro drug release were used to simulate the release performance of INS-loaded complexes. The release mechanism of INS from the complexes and the feasibility of MMT as the sustained-release drug carrier were discussed. The results showed that MMT had a high absorbability. In vitro release ability of INS from the complexes was affected by pH value of the release solution. The maximum concentration and the in vitro cumulative amount of INS released from the complexes at pH 7.4 reached 181.713 mg/L and 14.54%, and the lowest is at a pH value of 5.0. The first order kinetics model was better used to describe the variation of in vitro release rate of INS with time at different pH values, compared to the Korsmeyer-Peppas and Higuchi models. It is suggested that the release process of INS from the complexes in various solutions mainly depends on the physical diffusion