The miscibility of blends of poly(styrene-co-acrylonitrile) (SAN) and partially imidized poly(styrene-co-maleic anhydride) (SMI) was investigated using differential scanning calorimetry. SMIs with various contents and chemical structures of the imide unit were used in this study. The SANs whose acrylonitrile content is 20-32 wt% were miscible with these SMIs. It was observed that the type of substituent on the imide in SMI also affects the miscibility of the blend.