Ion beam assisted deposition (IBAD) techniques have been performed to synthesize ternary compound films composed of boron, carbon and nitrogen atoms (BC x N y ). BCN coatings were deposited on Si wafers and Si 3 N 4 disks by evaporating B 4 C target, with simultaneous N ion bombardment. The composition and chemical bonding were analyzed by XPS and the nanohardness was measured by Nano Indenter. The friction and wear property of the BCN coatings against Al 2 O 3 , SiC, Si 3 N 4 and SUS440C balls was investigated in air, N 2 gas and water, respectively. The worn surfaces on the BCN coatings and the balls were observed by optical microscope. The results showed that, the atomic ratio in the BCN coatings was 49 at.% B, 42 at.% C and 9 at.% N and there were several bonding states such as B-N, B-C and C-N with B-C-N hybridization in the BCN coatings. The nanohardness of the BCN coatings was 33 GPa. As the BCN coatings slid against ceramic balls, the friction coefficients in air were largest, while those in water were smallest among three kinds of environment. But as the BCN coating slid against the SUS440C ball, the friction coefficients in N 2 gas were slightly higher than those in air, whereas the friction coefficients in water also exhibited the lowest values. Among four kinds of tribo-pairs, the BCN/Al 2 O 3 tribo-pair showed the largest friction coefficient of 1.13 in air, but the BCN/Si 3 N 4 tribo-pair exhibited the smallest friction coefficient of 0.64 in N 2 gas and 0.03 in water. The specific wear rates of the BCN coatings were largest in N 2 gas, while lowest in water in all cases. The observation of worn surfaces on the BCN coatings and balls showed that the many roll-like materials were produced during sliding tests in air and N 2 gas, while the smooth surfaces were formed in water. The experimental results indicated that the interface reaction between the BCN coatings and water or oxygen had many influences on the friction and wear property of the BCN coatings.