Steady-state and time-resolved fluorescence measurements, using pyrene as probe, have been employed to study the contribution of hydrophobic interactions to the stabilization of polymer complexes. Complexes are formed in aqueous solutions through hydrogen bonding. Binary complexes have been studied between poly(acrylic acid) (PAA) and one of the four following polymers: poly(N-isopropylacrylamide), (PNIPAAM); poly(acrylamide), (PAAM); poly(vinyl methyl ether), (PVME); and poly(ethylene glycol), (PEG). From the results obtained, it was concluded that the PNIPAAM/PAA and PVME/PAA interpolymer complexes demonstrate a strong hydrophobic character, that the PEG/PAA complex demonstrates only a limited hydrophobicity, and that the PAAM/PAA complex is not at all hydrophobic.