Abstract: The friction and wear tests of a Cu-Zn alloy/SAE52100 steel pair and a quenched SAE52100 steel/tempered 5210 steel pair were conducted on a pin-on-disc test rig and an end-surface friction and wear tester under dry sliding and oil-lubricated sliding, respectively. The sequence signals of the frictional forces and vibrations were collected. The fractal behaviors of the frictional force and vibration signals were studied making use of correlation dimension. The results showed that the sequence signals of the frictional forces and vibrations had fractal characteristics, and the fractal dimensions of the signals varied with the test duration. The correlation dimension increased gradually for the "converging" (or running-in) friction and wear process, while it decreased gradually for the "diverging" friction and wear process. Moreover, the fractal dimensions of the frictional forces and vibrations varied in the same changing law as that of the worn surface morphology.