Cobalt (10 wt %) was supported on KOH-activated Ca-type montmorillonite (Ca-MMT) as a catalyst for Fischer-Tropsch (FT) synthesis. The material was systematically characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence (XRF), scanning electron microscopy (SEM), N-2 adsorption desorption at low temperature, temperature-programmed reduction of hydrogen (H-2-TPR), and temperature-programmed desorption of ammonia (NH3-TPD) techniques. It was found that the acidity and textural properties of the activated MMT were strongly dependent upon the conditions of alkaline treatment (concentration of KOH solution, time, and temperature), which determines the reduction behavior of the cobalt oxide and, thus, the conversion of CO and the selectivity of FT products. As a result, efficient Co/MMT catalysts for FT synthesis were obtained by optimizing the alkaline treatment of MMT.