Abstract: In the evolution of high-level radioactive waste repository, colloids will be produced when groundwater contacts the bentonite which is used as the buffer and backfill material in the near field of the repository. Therefore, extraction and characterization of the bentonite colloids are of great importance for understanding the diffusion and migration behaviors of key radionuclides. In this paper, Gaomiaozi bentonite and deionized water were used and boiling dispersion method was developed to extract bentonite colloids, and multiple analytical techniques were used to characterize the properties of the colloids. X-ray diffraction (XRD) analysis shows that the main mineralogical composition of the colloids is montmorillonite, which is confirmed by high resolution transmission electron microscopy (HRTEM) information. The average equivalent circle diameter and zeta potential of the colloids are obtained as 94 nm and -45 mV respectively by dynamic light scattering(DLS), suggesting that the colloids have good stability. Atomic force microscopy(AFM) results show that the mean diameter and height of bentonite colloids are (90±27) nm and （16.6±2.6）Å（1 Å=0.1 nm） respectively and the 2/3-layer hydrate exhibits the most ordered layer stacking. The average pH_PZC of the bentonite colloids is around 9.9 from the results of acid-base titrations.