The effect of chemical pretreatment on the chemical characteristics of steam explosion pulps was studied by ESCA, FTIR and other chemical methods. 18 different chemical solutions, which were the combination of following chemicals Na2SO3, NaOH, NaHCO3, Na2CO3, MgCO3, MgCl2, ZnCl2, Na2S or H2O2, were used as pretreatment agent. The chemical characteristics of pulps with different pretreatment including hydrophilic group content, surface composition of the fibers, bulk chemical composition as well as physical and optical properties were compared. Compared to Na2SO3alone or to other chemical pretreatment systems, a presence of NaOH, NaHCO3or MgCO3led to a higher hydrophilic group content, more carbohydrates exposed on the fiber surface as well as to a higher degree of lignin sulfonation, which may explain their high physical strength. A lignin analysis showed little difference in their bulk lignin contents. The presence of NaOH in impregnation solution led to xylan partially dissolving during the steam explosion cooking process. Furthermore, controlling the impregnation solution's initial pH in the range 9–10 normally led to high pulp yield.