The structures of poly (vinyl alcohol) (PVA)/Poly (vinyl pyrrolidone) (PVP) blends with different compositions prepared by solution casting method were investigated by Small Angle X-Ray scattering (SAXS). Results indicated that the structural parameters of the blends were deeply dependent on both compositions and crystallization conditions. According to one dimension electron density correlation function proposed by Vonk and the concept of pseudo two-phase strutural model

we obtained that the long periods and the thichnesses of transition layer increased with increasing the content of PVP in PVA/PVP blends while crystallinity

thicknes-ses of crystal lamellae of PVA/PVP blends and spcific inner surface decreased. Annealing process made the crystallinity strengthen obviously. The densty difference of crystalline and amorphous regions were about 0.005g/cm3 at all the ratios of compositions.