In the liquid phase methanol synthesis process, syngas reacts in the presence of fine catalyst particles slurried in the oil phase, in a three phase slurry reactor system. A method for activating high concentration (>25 wt.%) of the CuO-ZnO-Al2O3 catalyst in the catalyst-oil slurry has been successfully developed. This catalyst activation process can be of crucial significance in the research and development of the methanol synthesis process in a liquid entrained reactor. The reducing gas contains 2% hydrogen in nitrogen mixture and this activation procedure is carried out at a pressure of 125 psi. The catalyst-oil slurry is subjected to a controlled temperature ramping from 110 degrees to 250 degrees C. The catalyst has been shown to be effectively reduced after following this activation procedure, that is valid especially for high catalyst loadings in slurry. Since the reduction is carried out in the process liquid medium and inside the reactor system, the catalyst-oil slurry after the treatment is ready for the synthesis of methanol.