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The utilization of homogenous catalyst in the removal of naphthenic acids (NAs) had resulted in the emulsion problem in the reaction which will limit the percentage of total acid number (TAN) reduction. The emulsion formed will affect the quality of oil produced which will lower the price of the crude oil. In this study, the heterogeneous catalyst of Ni-doped Ca(10:90)/Al2O3 was studied for the catalytic extraction reaction in order to lower the Total Acid Number (TAN) in the crude oil to lower below 1.00 mgKOHg−1 utilizing 2-methylimidazole with the aid of Ni/Ca(10:90)/Al2O3 catalysts. Incipient Wetness Impregnation (IWI) methods was used to supported catalyst on the alumina and calcined at various temperatures of 800, 900, and 1000°C. Ni/Ca(10:90)/Al2O3 catalyst was characterized by using Thermogravimetry Analysis-Differential Thermal Analysis (TGA-DTA), X-ray Diffraction Spectroscopy (XRD), Brunauer-Emmett-Teller (BET), and Fourier Transform Infrared Spectroscopy (FTIR) to study the physicochemical properties of the catalyst. The results show that Ni/Ca(10:90)/Al2O3 catalyst successfully reduced the number of acids in crude oil to lower than 1.00 mgKOHg-1. Ni/Ca(10:90)/Al2O3 catalyst reduced TAN to 0.65 mgKOHg-1 of crude oil from original TAN of 4.22 mgKOHg−1 at 1000°C calcination temperature and catalyst loading of 7 beads (0.39%). XRD results proposed Al2O3 face-centered cubic (fcc) as an active site for Ni/Ca(10:90)/Al2O3 catalyst even though the surface area, average pore volume, and pore diameter were lower at calcination temperature at 1000°C. Stretching of N-H imidazole from 2-methylimidazole, C-H stretching from the NA species, and pure metal oxides (M=O) stretching modes were detected on Ni/Ca(10:90)/Al2O3 catalyst at a wavelength of 1455.96, 2952.2 to 2852.61 and 566.12 cm−1 respectively by FTIR analysis. FTIR result for spent catalyst after catalytic extraction process have impurities adsorbed on the surface of catalyst after a second cycle of reaction. [ABSTRACT FROM AUTHOR]