Flexible bearing is an important part of a harmonic gear reducer. In order to study the failure characteristics of flexible bearings, a special testing machine performing fatigue life experiments for flexible bearings was developed. The loading device of this testing machine can rotate with the inner ring of the flexible bearing and apply loads at both ends of the major axis of the outer ring synchronously. Several failure phenomena of flexible bearings were observed by the fatigue life experiments with four sets of flexible bearings. The width, depth and surface roughness of the raceways were measured after the experiments. The experimental results showed that wear and fatigue spalling behavior appeared only at the end of the major axis of the inner rings, and fatigue fracture and spalling might occur on the outer rings. Moreover, it was found that the wear of the raceways was not uniform.