A graphical multiple-peak resolution method for wide-angle x-ray scattering (WAXS) patterns is described and used to estimate the apparent crystallinities relative to the entire sample (Xca) in polymethyl methacrylate-polyethylene oxide graft copolymers (PMMA-g-PEO) and their ionic complexes with LiClO4, KSCN and FeCl2. The crystallinities (Xcg) and crystallite sizes (L120) in the PEO graft component, alone, were estimated at the same time. A concept of “reduced degree of crystallinity (Rc)” and “critical PEO content” is proposed and applied as a yardstick of the effects of PMMA backbone chains and salts on the crystalline behavior of the PEO graft chains.XcaandXcgincrease with both the content and molecular weight of the PEO graft chains. The critical PEO content, below which PEO crystallinity is not seen, is about 23.7%. PMMA backbone chains can reduce the crystallization of the PEO graft chains at any given PEO content.XcaandXcgdiminish after complexing with the salts and the order of reducing crystallinity is: LiClO4 > KSCN > FeCl2; salts have two inverse effects, reduction and promotion, on the crystallization of the PEO graft chains. The salt effects depend on the salt concentrations and coordination of the cations. The crystallite sizes in the PEO graft chains are smaller than those in the PEO homopolymers but increase after complexing with salts. The PEO crystallite sizes are not noticeably affected by the content and molecular weight of the PEO graft chains but are noticeably affected by salt concentration.