This paper explored the feasibility and benefit of CO2 utilization as gasifying agent in the autothermal gasification process. The effects of CO2 injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO2/C ratio from 0.6 to 1.6. O2 was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO2 injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO2-O2 gasification with a CO2/C ratio of 0.6–1.2. The progress of the expected CO2 to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO2/C ratio increased. The producer gas heating value of CO2-O2 gasification was consistently higher than that of air gasification. These results show the potential of CO2-O2 gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.