Pyrolysis is an efficient way of thermally converting biomass into fuel gas, liquid product and char. Inthis research, pyrolysis experiments were carried out in a circulating fluidized bed reactor with a riser diameter of 25mmand height 1.65m. The biomass used was corn cobs. The experiments were conducted systematically using two levelfactorial design with temperature ranging from 650 to 850 degree Celsius, corn cobs and catalyst contents in feed rang-ing from 0 to 100%, and from 1 to 5wt%, respectively, and Ni loaded on catalyst ranging from 5 to 9wt%. The resultsshowed that when temperature and catalyst contents in feed and Ni loaded on catalyst increased, the percent of hydro-gen and carbon monoxide increased. The amount of corn cobs was found to have an effect only on the compositionof hydrogen. Carbon dioxide was also observed to increase slightly. On the other hand, the percent of methane wasconsiderably decreased. The optimum conditions were 850 degree Celsius, corn cob content in feed of 100%, catalystcontent in feed of 5% and Ni loaded on catalyst of 9%. At this condition the percentages of hydrogen and carbon mon-oxide were 52.0 and 18.0, respectively.