Abstract: Seven partial demineralized coal samples （which basically contain only silicon and alumina minerals）were studied. The raw coals with different ranks were treated with HCl and HNO₃. The transformation behavior of sulfur in coals to char and the influence of silicon, aluminum and carbon were studied through a temperature programmed decomposition (TPD) and a temperature programmed oxidation (TPO) process. The results reveal that both the carbon content and the weight ratio of Si/Al affect the sulfur retention ratio in char. The retention ratio of sulfur in char increases with the increase of carbon content, but it reverses when the carbon content is around 90%. It is attributed to the significant change of the sample structure around this carbon content. For the acid treated coals from the same rank, the sulfur retention ratio in chars decreases with the increase of Si/Al weight ratio due to the inhibition effect of silicon on the secondary reaction between the gaseous sulfur-containing components and the char.