Complexation between poly(styrene-co-4-vinylphenol) (STVPh) and poly(styrene-co-4-vinylpyridine) (STVPy) in solution has been studied by a combination of static and dynamic laser light scattering. It was found that the complexation was strongly influenced by the phenol and pyridyl contents and the solvent used. In a stronger proton-acceptor solvent, the complexation only happens when the phenol and pyridyl contents are higher than a certain value, indicating a competition between the formation of the polymer-polymer and polymer-solvent hydrogen bonding. The addition of water, a strong hydrogen-bonding solvent, can completely destroy the complexation, clearly showing that it is the hydrogen bonding that induces the complexation. When the molar ratio of the monomer units of STVPh to STVPy is similar to 1:1, the scattering intensity reaches a maximum, indicating that the complexation has a 1:1 stoichiometry. On the other hand, when STVPy was in excess in the solution mixture, each STVPh chain is complexed with a certain number of the STVPy chains over a wide range of composition and vice versa, suggesting the complexation is sterically governed.