Ternary polymer blends of polyamide 6 (PA6), polycarbonate (PC), and phenol novolac (PN) were prepared by a melt mixing process. PN catalyzes the exchange reaction between PA6 and PC and promotes the generation of a copolymer, which improves the compatibility. Herein, the catalytic effect of PN was experimentally supported by an increase in torque during melt mixing and mass signals from copolymer fragments detected by mass spectroscopy. The characteristic behavior of the exchange reaction changed significantly with increasing PN amount. The promotion of in situ copolymer generation led to the formation of ternary blends, which show homogeneous morphologies and superior mechanical properties, such as high stiffness and good elongation, compared with those of the binary blends without PN. Using excess PN causes some drawbacks like brittleness due to the decomposition of the PC component. A loading amount of 1-3 wt % PN was suitable for achieving a ternary blend with improved properties.