The friction properties of aluminium-based composites containing a cluster diamond both in air and in vacuum were studied. In both cases, the coefficients of friction tend to decrease with the increase of the cluster diamond content in the samples. The coefficient of friction in air is lower than that in vacuum. After friction tests, atomic force microscopy and lateral force microscopy were used simultaneously to observe the surface friction process of the sample. A unique phenomenon is found : at some microconvex areas, the coefficients of friction are significantly lower. Scanning electron microscopic studies reveal that wear debris are formed during friction test with samples containing a cluster diamond. One of the significant factors for the reduction of friction could be the rolling effect caused by cluster diamond ultrafine particles.