The miscibility of nylon-6 with poly(4-vinylphenol) (PVPh) or poly(1-hydroxy-2,6-methylphenylene) (p-Cl-novolac) was studied with differential scanning calorimetry and small-angle X-ray scattering techniques. Both PVPh and p-Cl-novolac are miscible with nylon-6 at the molecular level. The presence of the phenolic polymers affects the crystallization of nylon-6 and suppresses its melting point. PVPh increases the long space order in crystalline nylon-6 because it increases the thickness of the amorphous layers. In contrast, a small quantity of p-Cl-novolac tends to decrease the long space order. It seems that p-Cl-novolac distributed in the amorphous regions introduces more order in these regions and makes the amorphous layers thinner. (C) 2001 John Wiley & Sons, Inc.