An environmentally benign process was developed for the production of biodiesel from cotton-seed oil using KF loaded with MgO as a heterogeneous solid super base catalyst. The 20 wt% KF/MgO, after desiccated at 120 oC for 4 h, was found to be the optimum catalyst. Hammett indicator method, XRD, SEM and IR were employed for the catalyst characterization. The results showed the activity of the catalysts was correlated with their basicity. The influence of various reaction variables on the conversion, such as the molar ratio of methanol to cotton-seed oil, the catalyst amount, the reaction time and temperature were also discussed. When the transesterification reaction was carried out at reflux of methanol (65 oC), with a molar ratio of methanol to cotton-seed oil 12 : 1, a reaction time 2.5 h and a catalyst amount 2.5 wt%, the highest conversion of cotton-seed oil reached 99.14%.