The miscibility behaviour of various poly(styrene-co-methacrylonitrile) (SMAN)/polymethacrylate blends was studied using differential scanning calorimetry. SMAN is miscible with poly(ethyl methacrylate) (PEMA), poly(n-propyl methacrylate) (PnPMA) and poly(isopropyl methacrylate) (PiPMA) over certain copolymer composition ranges, but is immiscible with poly(n-butyl methacrylate) (PnBMA) and poly(isobutyl methacrylate) (PiBMA). The width of the miscibility window decreases with increasing size of the pendent ester group of the polymethacrylate, and is wider than that of the corresponding poly(styrene-co-acrylonitrile) blend system. Various segmental interaction parameters are calculated using a binary interaction model.