Abstract: In this paper author tried to show the relationship between CO2 emission and GDP in panel data during 1960-2016 for four economies namely, USA, China, India and Japan through the methodology of fixed effect panel regression, Fisher-Johansen cointegration and vector error correction model with hypothesis of decoupling to justify EKC. The paper found that one per cent increase in GDP of USA, China, India and Japan led to 0.445 per cent increase in CO2 emission per year significantly during 1960-2016 in the fixed effect model of panel regression. In the decoupling model under panel regression during the same period it was found that the elasticities of CO2 emission with respect to GDP, GDP2, GDP3 and GDP4 were -8.94, 2.45, -0.262 and 0.0098 respectively all of which are significant at 5% level.