In this work, metformin HCl was encapsulated on citric acid activated montmorillonite as drug delivery system. The as-synthetized drug delivery systems were characterized by using FTIR and X-ray diffraction. FTIR spectra showed the presence of bending vibration of N-H from primary amines group and streching vibration of C=N at 1635.64 and 1506.41 cm -1 , respectively. X-ray diffraction pattern also showed a widening of the diffraction peaks of montmorillonite after encapsulated by metformin HCl. In vitro drug release results showed that the release of metformin HCl from the drug delivery system in simulated intestinal fluid (pH 7.4) higher than that in simulatied gastric fluid (pH 1.2) with a value of drug release of 61.44 % and 39.41 %. Metformin HCl release kinetics at each pH follow the zero-order model (pH 1.2 with R = 0.9924; pH 7.4 with R = 0.9972) suggested diffusion-controlled release mechanism.