A series of polystyrene-random-poly(methyl methacrylate) (PS-r-PMMA) copolymers with different compositions, adsorbed from toluene onto silica, were studied with modulated differential scanning calorimetry (MDSC). The equilibrium adsorbed amount increased monotonically with an increase in the methyl methacrylate (MMA) content in the copolymers. From the derivative MDSC curves, dC(p)/ dT vs T, the thermal transitions of the adsorbed chains were found to be dependent on the composition of the copolymers and representative of films with chain segments which were spatially heterogeneous. The intensities of the thermal transitions associated with more-mobile fractions in the polymer films decreased, and those associated with the more-rigid fractions increased when the MMA content in the copolymers increased. These changes were attributed to the strong interaction between MMA units and silanol groups on the silica surface. In addition, for the polymers studied, the relative intensities of the transitions associated with the more-mobile segments increased with increases in the adsorbed amounts.