In this paper, rotating-bending fatigue tests of short carbon-fiber reinforced polyetheretherketone (CFRPEEK) and polyetheretherketone (PEEK) were carried out to investigate the fatigue characteristics of plain and notched specimens at room temperature. The fatigue mechanisms in the matrix and composite was clarified through the successive surface observation using the replica method. The results were discussed using linear notch mechanics. In the plain specimen of PEEK, fracture always occurs from defects and the fatigue crack initiation is of the point-initiation type. Furthermore, the fatigue crack growth rate is very high and the fatigue strength is very sensitive to a notch. The fatigue strength of the composite is much more insensitive to a notch than that of PEEK. In general the fatigue crack initiates from near the fiber end, and propagates to the circumferential direction after it grows to some extent along the fiber. The fatigue strength of an arbitrary notched specimen of these two materials will be estimated from the present results rearranged based on 'linear notch mechanics'.