Abstract: The fretting wear experiments were made on nitrogen imp-larted samples and unimplanted samples of 9Crl8Mo steel respectively in this in vestigation. SEM was used to observe the topography of the fretted surfaces. AES and micro-region X-ray diffraction were also used to deter" mine the elements distribution and phase construction of the implanted surface tilm and wear track surface. The results have shown that the fret-ting wear resistance of the steel was obviously increased after implanting nitrogen ion, and the fretting wear mechanism was altered. Nitrides were formed in the nitrogen implanted surface film. The precipitation of these nitrides has some contribution to the enhancement of the fretting wear resistance of 9Crl8Mo steel.