Two semicompatible polymer blends, poly (vinylidene fluoride)/poly (ethyl methacrylate) (PVF2/PEMA) and polystyrene/poly (vinyl methyl ether) (PS/PVME), were examined in relation with the extent of mixing of the two components in the blends. For PS/PVME blends, CH2Cl2-cast specimens are highly opaque at any temperatures, while benzene-cast specimens are transparent at room temperature and exhibit a reversible LCST type phase separation behavior. For the opaque (incompatible) specimens of both systems, no master curves of complex moduli can be obtained, while for the transparent (compatible) specimens of the latter, smooth master curves are obtained. These results suggest that a macroscopic phase separation has taken place in the CH2Cl2-cast specimens, but a moderate one in the benzene-cast specimens. However, even for such transparent benzene-cast specimens the log (isochronal moduli) versus composition curves are of sigmoidal shape. These results suggest that even in the transparent specimens the two components were not molecularly miscible but formed microphase separated domains of the size less than the wavelength of visible light. PVF2/PEMA blends also exhibit a reversible LCST behavior with the cloud point above 200°C, and hence, is compatible in an ordinary temperature range. However, the system shows some discrepancy from a usual linear logarithmic dependence of isochronal complex moduli on composition. This result may also suggest that a moderate phase separation is taking place even in the transparent (and compatible) region.