Cu-Zn based catalysts for the direct synthesis of dimethyl ether were prepared by the co-precipitation method, and the feeding rate of ammonium carbonate used as the precipitant was controlled in order to change the particle size of the active materials. SEM and XRD confirmed that the catalyst particles that were prepared have a small size when the precipitant is rapidly fed into the precursor solution. The crystal growth of the Cu-Zn based catalyst could be controlled by changing the feeding rate of the precipitant in the precipitation method, and the physical properties of the Cu-Zn based catalyst were improved by controlling the crystal growth rate in order to enhance the catalytic activity. The feeding rate of the precipitant solution was controlled in range of 1.5-10.0 ml/min in this study. When the feeding rate of precipitant was adjusted from 1.5 ml/min to 10.0 ml/min, the particle size of Cu-Zn catalysts decreased from 28 nm to 10 nm with increasing feeding rates of precipitant solution and their surface area increased from 28 m2/g to 80 m2/g. The conversion of CO obtained in the catalytic activity tests also increased from 13% to 60%. A high conversion of CO was obtained over the Cu-Zn based catalysts prepared by changing the feeding rate of the precipitate.