The mixing state in polyoxymethylene (POM) and terpenephenol (TPh) blends prepared by melt-blending has been studied by transmission electron microscopy (TEM), Fourier-transform infrared (FT i.r.) spectroscopy and high-resolution solid-state C-13 n.m.r. spectroscopy. On the basis of these morphological and spectral measurements, the following facts have been revealed : (i) POM/TPh (5/5) blend is homogeneous on a scale of a mu m; (ii) the intermolecular hydrogen-bonding interaction between POM and TPh makes their blends miscible; (iii) a level of this interaction exhibits a significant compositional dependence; (iv) the noncrystalline phase of POM is preferentially miscible with TPh, while a part of POM is still crystallizable; and (v) the size of the phase-separated domain for POM/TPh (5/5) blend is estimated to be ca. 1 nm in the noncrystalline phase by the H-1 spin diffusion analysis, suggesting the almost homogeneous mixing on a molecular level.