A series of activated carbons were prepared front agricultural waste corn cob by the chemical activation with zinc chloride (ZnCl2). The effect of process variables such as pyrolysis temperature, soaking time and ZnCl2/corn cob ratio (impregnation ratio) of the production of adsorbent was examined. The most important parameter in the chemical activation of corn cob with ZnCl2 was found to be the impregnation ratio. The percentage of micropore was observed to decrease at higher impregnation ratios. The pyrolysis (or activation) temperature is another important variable, which had a significant effect on the pore surface area evolution. Under the experimental conditions investigated the temperature of 773 K was found to be the optimal condition for producing high surface area carbons with ZnCl2 activation. This study showed that the ZnCl2 activation of corn cob was suitable for the preparation of activated carbons which are essentially microporous.