KF/gamma-Al2O3 catalysts were prepared by impregnation method and investigated for the transesterification of ethylene carbonate (EC) with ethanol to synthesize diethyl carbonate (DEC). The KF/gamma-Al2O3 catalysts were characterized by nitrogen physisorption, XRD and FT-IR techniques, and three new species: K3AlF6, KOH and K2CO3 were found on the catalysts. Experimental results indicate that KOH and K2CO3 are the major active species and K3AlF6 is inactive for DEC synthesis. Increasing the KF loading favors the formation of K2CO3 and consequently enhances the activity of the KF/gamma-Al2O3 catalysts. However, when KF loading exceeded 50 mmol/g, the activity of the KF/gamma-Al2O3 catalysts decreased. This may be due to the presence of intact KF on the catalyst, which may dilute the content of active species in the catalyst and cover the active species. The KF/gamma-Al2O3 (50 mmol/ g) catalyst exhibits the best catalytic performance. With this catalyst, a 72 mol% yield of DEC ( based on EC) was obtained at 298 K.