This paper provides an alternative use of input-output structural decomposition analysis to identify the key factors that affected CO2 emission changes of Taiwan's petrochemical industries during 1984-1994. Changes in CO2 emission are decomposed into eight factors by integrating index decomposition analysis, input-output theory, and structure decomposition approach (SDA). The empirical results show the relative contribution of each factor on industrial CO2 emission change. Moreover, some policy implications are also elaborated based on the empirical results. This work is helpful for the framing of individual industrial CO2 reduction measures, and also provides a valuable reference for planning of national integrated CO2 mitigation.