Reactive blending of poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) with a catalyst mechanically dispersed on polymers was performed by one-step extrusion for about 1 min at 275 degrees C. The product appeared to be a transparent amorphous plastic with a single glass transition temperature. This approach provides a possibility to produce PET/PC block copolymers directly by extrusion of homopolymers or to create their compatible blends during one-step extrusion by varying the type and concentration of the catalyst.