Poly(3-carboxypropylmethylsiloxane) (PSI100) and poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X = 76, 60, 41,23 or 9, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the copolymer) were synthesized and characterized. PS19 is immiscible with both poly(4-vinylpyridine) (P4VPy) and poly(2-vinylpyridine) (P2VPy). The other PSIX samples are miscible with both P4VPy and P2VPy over the entire composition range. The shape of glass transition temperature (T-g)-composition curve of the miscible blend system changes from concave to S-shaped and to convex with increasing carboxylic acid content of the copolymer. The T(g)s of PS1100/P4VPy and PSI100/P2VPy blends are higher than those calculated from the additivity rule. The miscible PSI23/P4VPy and PSI23/P2VPy blends underwent phase separation upon heating, showing a lower critical solution temperature behavior. The other miscible blends degraded before phase separation could be induced by heating. The specific interactions between P4VPy or P2VPy and PSIX were studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The carboxylic acid groups of PSIX interact with the pyridine nitrogens through hydrogen-bonding interactions.