We study the edge diffraction enhanced printability in x-ray nanolithography under both proximity and soft-contact printing conditions. Theoretical modeling shows that the gap dependence of the edge diffraction is closely related to that of the minimum linewidth described by the common Fresnel formula and that the edge diffraction can significantly enhance the image contrast of nanometer scale features. Experimental results are also presented to show high resolution and high aspect ratio printability. Furthermore, a method for fabricating ultrahigh resolution and dense structure is discussed based on edge diffraction enhanced printability with very thin absorber masks.