To increase the hydrogen (H-2) concentration in bio-syngas containing carbon dioxide(CO2), water-gas shift reaction (WGSR) is widely used. In this study, the effects of CO(2)concentration on the WGSR and unwanted side reactions were investigated by varying the operating parameters, such as the steam/carbon monoxide (CO) ratio, reaction temperature, and the gas-hourly space velocity (GHSV). Based on the obtained results, CO conversion and H(2)yield decreased with increasing CO(2)concentration, especially when the steam/CO ratio was lower than 3. This implies that to minimize the negative effect of CO(2)on WGSR, the steam/CO ratio should be 3 or higher. For any CO(2)concentration, the highest CO conversion and H(2)yield were obtained at a reaction temperature of 400 degrees C. Therefore, the temperature should be precisely controlled at 400 degrees C. As GHSV decreased, the CO conversion approached equilibrium with any CO(2)concentration; however, the H(2)yield remained unchanged.