Styrene-acrylonitrile random copolymer (SAN) and polyarylate (PAr) block copolymer were applied as a reactive compatibilizer for polyamide-6 (PA-6)/acrylonitrile-butadiene-styrene (ABS) copolymer blends. The SAN-PAr block copolymer was found to be effective for compatibilization of PA-6/ABS blends. With the addition of 3.0-5.0 wt % SAN-PAr block copolymer, the ABS-rich phase could be reduced to a smaller size than 1.0 mum in the 70/30 and 50/50 PA-6/ABS blends, although it was several microns in the uncompatibilized blends. As a result, for the blends compatibilized with 3-5 wt % block copolymer the impact energy absorption reached the super toughness region in the 70/30 and 50/50 PA-6/ABS compositions. The compatibilization mechanism of PA-6/ABS by the SAN-PAr block copolymer was investigated by tetrahydrofuran extraction of the SAN-PAr block copolymer/PA-6 blends and the model reactions between the block copolymer and low molecular weight compounds. The results of these experiments indicated that the SAN-PAr block copolymer reacted with the PA-6 during the melt mixing process via an in situ transreaction between the ester units in the PAr chain and the terminal amine in the PA-6. As a result, SAN-PAr/PA-6 block copolymers were generated during the melt mixing process. The SAN-PAr block copolymer was supposed to compatibilize the PA-6 and ABS blend by anchoring the PAr/PA-6 and SAN chains to the PA-6 and ABS phases, respectively.