In this study looks at the effect of the removal of polluting compounds, i..e. S,N,Hg and Cl from poor quality coals prior to combustion is investigated. This is important not only for improving the coal quality, but also for meeting the strict environmental standards. Thus, a preventive fuels pretreatment technique, based on low temperature carbonization, aiming to convert "dirty" fuels to cleaner ones, has been tested. Clean coals were produced from two Greek poor quality coals (Ptolemais and Megalopolis ) and an Australian coal sample, in a lab-scale fixed bed reactor, under helium atmosphere and ambient pressure. The effect of carbonization temperature (200-900°C) and residence time (5-120 min) on the properties of the obtained chars were investigated. Special attention was paid to the polluting compounds (S,N,Hg,Cl) removal. To account for possible mineral matter effects, mainly on Sulphur removal, tests were performed with demineralised coal also. The reactivity under combustion conditions of the chars produced was also investigated. It was observed that low temperature carbonization could contribute to clean coal production by effectively removing the major part of the existing polluting compounds in the coals. Thus, depending on coal type, nitrogen, mercury and chlorine conversion continuously increase with temperature, while sulphur removal seems to reach a plateau above 500-600oC. Furthermore, the prolongation of carbonization time above 20min does not affect the elemental conversion of the pollutants. Therefore, carbonization at 500-600oC for 20 min could be considered sufficient for clean coal production from poor quality coals. The reactivity of the prepared clean coals was evaluated by performing non-isothermal combustion tests in a TA Q600 thermo balance at ambient pressure and 20oC/min heating rate. At increased Pyrolysis temperatures higher initial combustion temperatures were observed, due to the volatile reduction in char production stage. The latter results to lower total conversions. Mineral matter removal, lead to increased char reactivity by increasing both the initial combustion temperature and the combustion rate.