High methanol/oil ratio together with reaction temperature with increase reaction time are some of the major drawbacks affecting the use of inorganic heterogeneous catalysts for simultaneous esterification and transesterification of oils. In this study, a novel bio-based bifunctional catalyst (BBFC) was prepared from sulfonated calcined corncobs and calcined poultry droppings by wet impregnation method. Characterization of the BBFC was done using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Its catalytic activity in simultaneous esterification and transesterification of neem seed oil (NSO) having high free fatty acid content of 4.426% was investigated, with process parameters optimized using response surface methodology (RSM). Result revealed that the BBFC is highly bifunctional, possessing both acidic and basic oxides. Biodiesel yield of 92.89 wt% with an acid value of 0.23 mg KOH/g was obtained at optimum conditions of methanol/oil ratio, reaction temperature and time of 14.76:1, 61.90 degrees C and 72.65 min respectively using a catalyst loading of 2.58 wt%. The economic viability of the catalyst was also investigated and results shows that using recovered catalyst from the process gave a biodiesel yield of over 89 wt% after two successive cycles. (c) 2020 Elsevier Ltd. All rights reserved.