Oxygen-enriched combustion of coal has so far been investigated using either entrained flow reactors or fluidized-bed combustors where burning takes place rapidly due to high heating rates. On the contrary, this paper presents the results of slow burning of coal under oxygen-enriched combustion conditions. Ashing behavior of mineral matter-rich low-rank coal from Turkish Tekirdag-Malkara lignite under oxygen-enriched conditions was investigated to determine the effect of this combustion technique on unburnt carbon, mineralogical characteristics and the burning performance. These experiments showed that the influence of O-2 concentration on ashing is much more evident than the temperature during oxygen-enriched combustion.