Abstract: Modes of iodine occurrence in bituminous coal and anthracite were investigated by using inductively coupled plasma mass spectrometry (ICP-MS) and sequential chemical extraction. The results showed that iodine in both these coals occurs in a descending order of organic, bound with Fe-Mn oxide, water-soluble, residue, ion exchangeable, and the fraction bound to carbonate. In bituminous coal and anthracite, the mean relative content values are 47.4%±3.28% and 43.3%±2.42% for iodine bound to organic matter, 36.8%±3.70% and 34.6%±4.77% for the iodine bound to Fe-Mn oxides, respectively; the amounts of water soluble and ion exchangeable iodine are 10.3%±3.00% and 14.3%±3.37%, respectively; the potential leachable rates of iodine are 10.9% and 16.0%, and potential leachable iodine contents 0.9 μg/g and 1.2 μg/g, respectively. These results suggested that iodine leaching from both these coals can lead to an increase of iodine concentration in surface water at the supergene conditions; the effect of iodine in anthracite is more environmentally favorable than that in bituminous coal.