Although Tocqueville hardly anywhere uses the term natural law in his writings, this article attempts to demonstrate not only that he acknowledges the existence of natural law but that the idea of this law plays a crucial role in his thought. In the first part, the article reconstructs the essence of his concept of natural law and its relation to positive law. The conclusion of this part is that Tocqueville’s idea of natural law is based mostly on the Catholic rational concept of this law. Moreover, the article focuses also on the relation between natural law and the most fundamental values of Tocqueville’s thought: virtue and liberty. In the last part, the article shows the importance of the natural-law concept in Tocqueville’s critique of socialism.