The miscibility between poly(styrene-co-4-vinyl benzoic acid), that is, carboxylated PS (CPS), and polyfn-butyl methacrylate-co-(4-vinylpyridine)] (BVPy) was investigated using differential scanning calorimetry (DSC). The results showed that, when the 4-vinyl pyridyl content in BVPy was higher than about 5 mol%, the CPS/BVPy system exhibited miscibility for the carboxyl content in CPS as it varied from 1.6 to 20 mol%. Complexation between CPS and BVPy in non-aqueous solutions was studied by viscometry. It was found that, when the density of hydrogen bonding between the proton-donating and the proton-accepting polymers reached a certain level, an intermacromolecular complex would form as turbidity and/or precipitate in organic solutions such as 2-butanone and THF. Combining the results from DSC and viscometry in 2-butanone, an immiscibility-miscibility-complexation map for the CPS/BVPy system was obtained.