In a series of essays published from the late 1920s up to the mid-1960s, Hans Kelsen carries out a radical critique of natural law theory. The present paper purports to provide an analytical reconstruction and a critical assessment of such 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 such criticisms.