Block copolymers of polycarbonate-b-poly-(methyl methacrylate) (PC-b-PMMA) and tetramethyl poly(carbonate)-b-poly(methyl methacrylate) (TMPC-b-PMMA) were examined as compatibilizers for blends of polycarbonate (PC) with styrene-co-acrylonitrile (SAN) copolymer. To explore the effects of block copolymers on the compatibility of PC/SAN blends, the average diameter of the dispersed particles in the blend was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) technique and an asymmetric double cantilever beam fracture test. The aver-age diameter of dispersed particles and interfacial tension of the PC/SAN blends were reduced by adding compatibilizer to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing interfacial adhesion with compatibilizer. TMPC-b-PMMA copolymer was more effective than PC-b-PMMA copolymer as a compatibilizer for the PC/SAN blends. (C) 2003 Wiley Periodicals, Inc.