The complexation of poly(styrene-co-vinylphenol) (STVPh) and poly(styrene-co-vinylpyridine) (STVPy) in nonaqueous solution was investigated with emphasis on the effect of the hydroxyl and pyridyl contents in the component polymers. Viscometry, nonradiative energy transfer fluorospectroscopy, and dynamic laser light scattering have led to the same conclusion, i.e., STVPh and STVPy blend can form an interpolymer complex due to hydrogen bonding in tetrahydrofuran, butanone, and chloroform, provided the contents of the hydroxyl and pyridyl reach certain respective levels. The size distribution of the complex aggregates is relatively narrow with a peak size 1 order of magnitude larger than those of the component polymer coils. The minimum content of the interaction groups required for complexation strongly depends on the solvent used. Chloroform and butanone are almost inert for hydrogen bonding between the polymers, tetrahydrofuran has a substantial influence on complexation, and addition of N,N-dimethylformamide into the dispersion of complex aggregates in THF even causes decomplexation.