A novel intumescent flame retardant: tetra-spirophosphoryl-benzoguanamine (TSPB) containing three constituents was used as a new flame retardant for polypropylene to prepare flame-retardant materials, whose flammability and thermal behavior were studied by the limited oxygen index (LOI), thermogravimetric analysis (TGA), in addition whose mechanical properties were investigated in this work. It was found that when the addition of TSPB was 25 wt %, the LOI value of the PP could achieve to 29.5 and pass the UL-94 V-0 rating test. The TGA data showed that TSPB could enhance the thermal stability of PP and effectively increase the char residue formation. The mechanical performance test showed that the addition of TSPB improve the mechanical performances of PP to some extent. Thus, the trinity intumescent flame retardant TSPB is good to modify PP. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2170-2177, 2010