A series of hydrotalcites with various Mg/Al contents were prepared by a solid state reaction. They were then calcined at 450℃ to form a series of Mgx-Aly-O catalysts with different Mg/Al ratios for use in the depolymerization of polystyrene (PS) in a batch reactor. The prepared catalysts were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray analysis (EDX), induced coupled plasma-atomic emission spectroscopy (ICP-AES) measurements. The characterization results showed that the Mgx-Aly-O mixed metal oxide catalysts were successfully synthesized as attempted in this work. Basicity of Mgx-Aly-O catalysts was determined by CO2-TPD measurement to elucidate the catalytic performance in the depolymerization of PS. It was found that basicity and catalytic performance (PS conversion, oil yield, and styrene monomer (SM) yield) showed volcano-shaped trends with respect to the Mg/Al ratio of Mgx-Aly-O catalysts. Correlations between basicity and catalytic performance revealed that all of PS conversion, oil yield, and SM yield were improved with the increasing basicity. Among the catalysts tested, the Mg1-Al2-O (Mg/Al = 0.5) catalyst with the largest basicity showed the best catalytic performance. Thus, basicity of Mgx-Aly-O catalyst played an important role in the determining the catalytic performance in depolymerization of PS.