The granite swarf produced by impregnated diamond bits were collected during micro-drilling experiments. The particle size distributions of the swarf were analyzed to quantitatively investigate the particle size distribution laws and the effects of diamond parameters and drilling parameters on the swarf size distributions. The results show that the particle size distribution of the granite swarf is consistent with logarithmic normal distribution. Most swarf particle sizes vary from 40 to 100 μm. Meanwhile, the swarf particle size distribution is influenced by the diamond size, diamond concentration, bit pressure and rotate speed.