In this study, the effect of coal comminution with waterjets enhanced by cavitation was investigated. The experiments were carried out using mono-size coal feeds in a batch closed circuit, in a specially designed cell to induce cavitation at 69 MPa inlet pressure and back pressures of zero and 0.345 MPa. Test results were evaluated on the product calculated surface area and the Rosin-Rammler parameters. The experiments showed that the maximum particle size reduction was achieved during the first run through the comminution circuit operated without back pressure. However, a decreasing tendency in comminution efficiency was noted with the number of runs through the system. The use of 0.345 MPa back pressure resulted in a wider size distribution of the product.