A magnesium-aluminum layered double hydroxide was synthesized with co-precipitation method and zinc salt was impregnated on it. The final product was calcined and used as a catalyst in the transesterification reaction to produce biodiesel from waste cooking oil. Both MgAl hydrotalcite and Zn impregnated compound (Zn/MgAl(O)) were characterized using X-Ray Diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) techniques. High surface area and nanometric pore size of Zn/MgAl(O) was determined using Bruneure-Emmett-Teller N-2 physisorption technique. Another fully co-precipitated ZnMgAl mixed oxide was synthesized by and compared with Zn impregnated product in the transesterification reaction. The reactions were performed at 65?C using 9:1 methanol to oil ratio for 3?h. The biodiesel yields were measured by gas chromatography (GC). Leaching amounts of surface active components of as-synthesized mixed metal oxides were determined by EDS and ICP analysis of used catalyst. Zn impregnated catalyst showed 78.45% conversion of the fatty acid to methyl esters and just 1.16% leaching of Zn was observed, that is much lower than the diminishing in the co-precipitated compound. Finally, the reaction and leaching proofs and the effect of synthesis method on the firmness of catalyst were discussed.