In a series of essays published from the late 1920s up to the mid-1960s, Hans Kelsen carried out a radical critique of natural law theory. The present paper purports to provide an analytical reconstruction and critical assessment of such a critique. It contains two parts. Part one surveys the fundamentals of Kelsen’s argumentative strategy against natural law and its theorists. Part two considers, in turn, two critical reactions to Kelsen’s criticisms: by Edgar Bodenheimer, on behalf of traditional natural law theory; by Robert P. George, on behalf of “the new natural law theory”. As the analysis suggests, Kelsen’s critique stands up to the criticisms.