This paper investigates the validity of the environmental Kuznets curve (EKC) theory affected by income inequality and the impact of income inequality, economic growth, population density, and energy use on environmental degradation in ASEAN. For this purpose, we utilise the biased corrected least squared dynamic variable (LSDVC) estimation approach using the sample of ASEAN-6 countries from 1992 through 2015. The finding confirms that the existence of EKC theory is affected by income inequality in the short and long term. It indicates that economic growth has different effect on the environment at different stages of development. Moreover, the outcome also emphasises that widening income inequality drives more environmental degradation in ASEAN-6 countries. Meanwhile, economic growth and energy use significantly impact the changes in environmental degradation. Hence, the member states of ASEAN should address unequal income distribution in the region with more consistent efforts and support to maintain environmental quality.