The phosphoric acid-pentaerythritol-melamine copolymer was selected as an intumescent flame retardant (IFR). The influence of dicromate acid-etching polypropylene (EPP) on the properties and compatibility of IFR/PP composites was studied. The results obtained from mechanical tests and SEM showed that EPP was a true coupling agent for IFR/PP blends, but without changing the necessary flame retardancy. The cocrystallization between bulk PP and PP segments of EPP was proved by WAXD analysis. Flow tests showed that the flow behavior of composites in the melt is that of a pseudoplastic liquid, which is almost insignificant fur EPP affecting the rheological behavior of an IFR/PP composite.