Iranian montmorillonite (MMT) was modified with hexadecyltrimethylammonium bromide (HDTB) and used as a nano-additive for the enhancement of the mechanical and anticorrosion properties of an epoxy coating. Infrared (IR) spectroscopy, thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis indicated that HDTB reacted with MMT (with 97% yield) and increased the d001 spacing of MMT from 1.27 to 3.92 nm. Some 1, 3 and 5 wt.% of organically modified montmorillonite (OMMT) were added to the epoxy coating formulation. XRD and TEM/image processing analysis showed that the extent of intercalation/exfoliation of OMMT was substantially greater than that of MMT. Dynamic mechanical analysis showed that the glass transition temperature and storage modulus increased significantly with the addition of OMMT. Electrochemical impedance spectroscopy (EIS) and salt spray/image processing results revealed that addition of OMMT to the epoxy coating significantly increased the corrosion resistance of the coating compared to neat and MMT-containing epoxy coatings. The optimum concentration of OMMT was 3 wt.%. At this concentration, the mechanical and anticorrosion properties were greatly superior to those of neat and MMT-containing epoxy coatings.