Gasification slag is a potential resource of high value, which can be utilized as a porous material by acidification. To have a deep understanding of the composition and structural characteristics of the acidified slag, the gasification slag was treated using different concentrations of acetic acid (HAc) and HCl, respectively. The slag samples, in both an untreated and an acidified form, were characterized by AAS, XRD, FT-IR, BET, and TG. The results show that the reaction between the slag and a higher concentration of HAc could generate crystal minerals like alumohydrocalcite (CaAl2(CO3)(2)(OH)(4)center dot 3H(2)O) and aluminum acetate hydroxide ((CH3COO)(2)Al(OH)). Meanwhile, HAc treatment results in an increase of crystallinity, but HCl treatment exerts the opposite effect. In addition, compared to the untreated, the specific surface area of the slag treated by HAc and HCl increases 20 times and 86 times, respectively. Acid treatment would make more mesoporous due to the extraction of Ca.