The optimum operating conditions of a single step synthesis of dimethyl ether (DME) from synthesis gas has been determined. The bifunctional catalyst has been prepared by physically mixing of a commercial methanol catalyst (KMT Co.) and a dehydration catalyst (H-MF-90) which has been characterized by XRD, XRF and BET techniques. Catalytic synthesis of dimethyl ether from synthesis gas was evaluated in agitated slurry micro reactor in different ranges of operating conditions which were determined by experimental design according to Taguchi algorithm. The range of operating conditions were chosen as follows: H2/CO mole ratio in feed varying from 0.26 to 1.5, the pressure varying from 10 to 50 bar, the temperature varying from 200 to 240 ºC and weight ratio of methanol catalyst to dehydration catalyst from 0.67 to 4. The experiments have been conducted for different operating conditions at fixed impeller speed equal to 1600rpm and space velocity equal to 500 ml/gcat.h. Considering the results of experiments, optimum conditions for direct synthesis of DME were predicted as follows: T=240 ºC, P=33.3 Bar, H2/CO=1.5 and weight ratio of methanol catalyst to dehydration catalyst equal to 3.