This paper is about the pretreatment of coal to remove mercury content prior to coal combustion. The minute amount of mercury in Pittsburgh No. 8 coal (0.177 ppm) was removed by flowing a gas stream containing 10% oxygen and 1000 ppm SO2 into a coal-water slurry at 30 mL/s. A total of 50 g of 35-65 mesh coal was leached each time in 500 mL of solution. The temperature was varied from 50 to 80 degrees C, and the initial solution pH varied at 5.7, 1.8, and 1.5. It was found that the mercury removal increased from 44.2% at 50 degrees C to 88.6% at 75 degrees C at the natural pH (5.7) and after 3 h of reaction time. The pyrite conversions were much lower than those of mercury. Both the mercury and pyrite removals increased as the pH decreased at 71 degrees C. Mercury removal was high enough to consider the application of this technology to a commercial process.