A series of boria catalysts supported on titania-zirconia mixed oxide (B2O3/TiO2-ZrO2) with different boria loadings (8-20 wt%) were prepared and characterized by X-ray diffraction, adsorption of nitrogen B-11 magic angle spinning (MAS) NMR measurements and temperature-programmed desorption (TPD) of ammonia. The catalytic performance of B2O3/TiO2-ZrO2 for vapor-phase Beckmann rearrangement of cyclohexanone oxime to epsilon -caprolactam was studied at 300 degreesC. It was found that the lactam selectivity increased with increasing of boria loading, whereas a maximum oxime conversion was obtained at the boria loading of 12 wt%. The acid sites of medium strength on the surface of the catalyst play an important role in the selective formation of lactam.