The use of Mg-montmorillonite in the production of organoclay without sodium activation was investigated. For this purpose, organophilization experiments were carried out by varying the concentration of two surfactants: hexadecyltrimethylammonium (HDTMA+) and dodecyltrimethylammonium (DTMA+) ions. These surfactants were used at concentrations 0.7, 1.0 and 1.5 times that of the cation exchange capacity (62.6 meq/100 g) of the clay, with a reaction time of 8 h at temperatures of 25 and 80°C. X-ray diffraction (XRD) results confirmed the intercalation for both in natura and activated samples. The Fourier-transform infrared (FTIR) spectroscopy and XRD results showed that the ratio of gauche/trans conformers decreased with increased basal spacing. The results of thermodifferential and thermogravimetric analysis (DTA/DTG) confirmed the thermal stability of the organoclay up to 200°C, permitting the use of such material in the synthesis of polymer/clay nanocomposites obtained by the melt blending. Thus, Mg-montmorillonite can be intercalated with alkylammonium ions without prior Na-activation to form organoclays. The possibility of using natural (non-activated) Mg-montmorillonite represents a significant difference in terms of processing cost in comparison with existing Ca-montmorillonite in Brazil or even with imported bentonites that require Na-activation during beneficiation.