The catalytic properties of KF/MgO for the synthesis of didodecyl carbonate (DDC) by transesterification from dimethyl carbonate (DMC) and dodecanol were studied. The effects of loading amount of KF and calcining temperature were systemically investigated. The phase structure was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Interaction between KF and the carrier MgO occurred in the process of calcination, and a new phase K2MgF4 formed when calcining temperature was 673 K or above. FTIR results showed that K2CO3 was observed when catalysts calcined in air. When calcining temperature was 873 K and the loading mass amount of KF was 30%, the KF/MgO catalyst exhibited the optimal catalytic properties and the yield of DDC was maximized to 80%. The excellent catalytic properties of KF/MgO was ascribed to the formation of K2MgF4+K2CO3 during the calcination in air.