This article aims to analyze the task of environmental protection and defense from the comparative perspective of the existence of a fundamental duty inherent to all Brazilian and Portuguese citizens as a result of the normative text presented in the constitutions of the two countries. We present data which proves that neither society nor the State adequately fulfill the fundamental duty of protection and defense of the environment. To solve the problem, the article presents a proposal for greater political and social participation of citizens through active citizenship, so that they could directly interfere in public policies, thus, fulfilling its fundamental duty to protect the environment.