Abstract: High yield of ethylene glycol (EG) can be obtainedby using the catalyst with 20% Cu loading, but the short life of the catalyst blocks its industrial application. This work focuses on the cause of the deactivation behavior. SiO₂ supported copper catalyst for gasphase hydrogenation of diethyl oxalate (DEO) was prepared using the ammoniaevaporation method. The catalyst was characterized by the means of X-ray diffraction (XRD), temperature-programmed reduction (TPR) and highresolution transmission electron microscopy (HRTEM). It was found that copper particles were highly dispersed on the surface of fresh catalyst in small size, and the aggregation of them was the main reason for deactivation. In addition, the results indicated that Cu⁰ is the main active site for the hydrogenation.