Various studies have been carried out on the effect of microwave-treatment on grinding different types of coal. However, the effect of microwave treatment on grinding coal samples -3.35 mm in size which can be considered to be fine is still under investigation. The purpose of this paper is to make contributions to these studies conducted. In the study, lignite coal samples with pyritic sulphur and 25% structural moisture were crushed below -3.35 mm particle size using jaw and cone crushers and then classified into three different mono size groups by Russel sieve. For a complete removal of the structural moisture from the lignite coal, a microwave application with 600W needs approximately 35% more energy consumption than that with 850 W. The untreated coal samples and the ones treated with microwave at 850W were ground for 5, 15, 30, 60, 120 s in a stirred media mill. The breakage rates of microwave-treated coal increased and accordingly the ground products of microwave-treated coal yielded finer particles than -106 mu m as compared to untreated coals. The untreated and microwave-treated feed coals of -3350 mu m and -1180 mu m particle sizes were ground for 2 min in the stirred media mill. It was found that the increases in the rate of weight percentages for -106 mu m particle size fraction after 2 min of grinding of untreated and microwave-treated feed coals of -3350 mu m and -1180 mu m were found to be 15.81% and 2.69%, respectively. Moreover, Hardgrove Index (HGI) test results of lignite coal showed that the HGI index value increased by approximately 23% after microwave treatment with 850 W. (C) 2010 Elsevier Ltd. All rights reserved.