Since montmorillonite (Mt) and organomontmorillonite (O-Mt) are widely used in many different areas from ordinary to high technological applications, there are lots of studies about them in the literature. However, its unique characteristic and different interaction mechanism with additives make those studies continue in order to explain much more detail on it In this study effect of hexadecyltrimethylammonium bromide (HDTMA) on Mt through modification process has revealed in detail. Adsorption, electrokinetic, rheology and structural aspects of the system were considered in together to explain the interaction mechanism between Na-Mt and HDTMA. Mt suspensions show four different characteristics that are dependent on the HDTMA concentration as dispersion, coagulation-precipitation, coagulation-flotation and re-dispersion. It is found that sedimentation behavior at this regions are in a good agreement with adsorption isotherm, zeta potential, apparent viscosity, X-ray diffraction patterns, swelling index and filtration losses. (C) 2016 Elsevier B.V. All rights reserved.