Flame-retardant hyperbranched pentaerythritol (FR-HPER) was prepared by condensation polymerization between pentaerythritol (PER), the monomer, and phosphate acid we prepared. It was then characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and matrix-assisted laser desorption ionization time of flight mass spectrometer (MALDI-TOF-MS). This FR-HPER was used in the preparation of natural rubber (NR)/FR-HPER composites. Different types of NR/FR-HPER composites were prepared with different amounts of FR-HPER, and compared with the composites directly incorporated with PER. Then, the tensile, wear resistant, thermal, and FR properties were researched and compared. Results showed that some mechanical and FR properties of NR/FR-HPER composites showed obvious improvements compared with that of NR and NR/PER systems. Schemes of toughening, wear resistant, and FR mechanism were proposed. The hyperbranched polymer may reduce the amount and size of voids in NR matrix, and thus increase the tensile properties. Meanwhile, the synergistic effect between nitrogen in PER and phosphorus in phosphate acid can increase the amount of carbonaceous layers, and thus may inhibit the pyrolysis degree of NR matrix during burning. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013