Polyurethane elastomer (PUE) was firstly applied to mining coal roadway as air-leak sealant. It is very important for air-leak sealants to possess the super mechanical properties and good flame retardant performance when applied to the coal-rock mass with cracks. The reinforced and toughened PUE nanocomposites were obtained by adding surface modified TiO2 and SiO2 nanoparticles. The modified PUE was characterized in terms of morphology, structure, and thermal stability by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Its flame-retardant performance and mechanical properties were also tested. The results showed that the surface modified nanoparticles were uniformly dispersed in the PUE matrix and enhanced its thermal stability and flame retardant performance. The dual effects of uniform dispersion of nanoparticles and hydrogen bonding between nanoparticles and PUE improved the mechanical properties of the composites. The PUE modified by nanoparticles was successfully applied to coal mines and showed great air-leak sealing effect. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013