The present study aims to offer a reflection on moral responsibility and legal responsibility. Moral responsibility will be based on thomism, specifically in Doctrine of double effect. With regard to legal responsibility, we will discuss the morality of law in Lon Fuller. In the first chapter we will study the Doctrine of double effect, also known as Theory of double effect, which has its roots in thomistic moral philosophy, by studying the conditions under which an action with good and bad results is morally permissible. In the second chapter, we will study about law and its morality, where we will take as basis for the concept of natural law according to Lon Fuller. We will notice that Fuller considers that the quality of law will depend on its internal morality. Finally, in the third chapter, based on the work of Lon Fuller: The case of the exploiters of cave, we will introduce a summary of the work and an analysis of the book under the Doctrine of double effect s point of view and criminal law Brazilian s either. We will complete this study speaking of the choice and its moral responsibility and the legal responsibility and the levy of law.