As the country with the second largest emitter of energy-related CO2 gas, China experienced a dramatic decline in CO2 emission intensity from 1991 to 2000, but since then the rate of decline slowed and CO2 emission intensity actually increased in 2003. In this paper, the complete decomposition method developed by Sun is used to analyze the nature of the factors that influence the changes in energy-related CO2 emission and CO2 emission intensity during the period 1991-2006. We find that: (1) energy intensity effect is confirmed as the dominant contributor to the decline in CO2 emission and CO2 emission intensity, (2) economic activity effect is the most important contributor to increased CO2 emission, and (3) economic structure and CO2 emission coefficient effects are found to contribute little to the changes in CO2 emission and CO2 emission intensity, which actually increased CO2 emission and CO2 emission intensity over the period 1991-2006 except for several years. (C) 2008 Elsevier Ltd. All rights reserved.