Polycarbonate (PC) blended with acrylonitrile-butadiene-styrene (ABS) has the maximum notched Izod impact strength, which is 58 kg cm cm(-1) for PC/ABS1 and 66 kg cm cm(-1) for PC/ABS2, at a ratio of 80/20 in this study. We selected the ratio of 80/20 to prepare frame-retardant PC/ABS alloys. The compatibility of flame-retardant PC/ABS alloy was examined by differential scanning calorimetry (DSC). The flame-retardant PC/ABS alloy had two values of the glass transition temperature (T-g), indicating that the alloy was not compatible. Three kinds of compatibilizers, methacrylate-butadiene-styrene (MBS), ethylene-vinyl acetate (EVA), and styrene-maleic anhydride (SMA) were used to improve the phenomenon. DSC measurement revealed that after compatibilization the alloy had only one value of T-g, meaning that the alloy became more compatible. Samples were frozen in liquid nitrogen to look at their morphology. We found that the domain sizes were reduced and the surface boundaries were closed and blurred, a feature that could promote the mechanical properties of the alloy. In this study, we also compared the effects of mechanical properties on differential compatibilizers for the flame-retardant PC/ABS alloy. Cycoloy 2800 is a commercial-grade flame-retardant product and was chosen to compare it with our prepared alloys in this study.