In this paper, Ca2+-montmorillonite (Ca2+-Mt) was modified with cationic surfactant hexadecyl trimethyl ammonium Bromide (CTAB) directly, without changing Ca2+-Mt into Na+-montmorillonite (Na+-Mt). X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), contact angle tests and rotary viscosity tests were used to characterize the structure and property of the organo-montmorillonite. The results of XRD show that interlayer space (d001) of the product is 4.05nm. The results of TGA indicate the ratio of weight loss of the organic components in the product is 37.7%. The results of FT-IR indicate there are organic components and hardly any water molecules in the product. All these findings indicate that the CTAB has intercalated into the galleries of Ca2+-Mt. Contact angle tests shows the product is well hydrophobic and the hydrophobic property is as good as that of organo-montmorillonite modified from Na+-Mt. Rotary viscosity tests show that the viscosity of the product at the rotational speed of 6R/min is 1226mPa·s, much better than that of the organo- montmorillonite modified from Na+-Mt which is 1070 mPa·s. The thixotropy index of the product is 9.22, much better than that of the organo-montmorillonite modified from Na+-Mt which is 5.88. It can be concluded that organo-montmorillonite with perfect interlayer expansion and thixotropic property was prepared by modifying Ca2+-Mt with CTAB directly.