AbstractThe composition of polymer blends and alloys and the crystallinity and crystallite size/perfection of each of the components are determined by X‐ray diffraction (XRD) methods. A profile‐fitting procedure is used to resolve the XRD scan into crystalline and amorphous peaks corresponding to each of the polymers. The procedure uses templates derived from the XRD scans of the homopolymers as constraints. The usefulness of this method for studying the influence of blending and grafting is illustrated by analyzing the data from two‐component blends with and without the graft copolymer compatibilizer.