An acid photocatalyst TiO2, modified with H2SO4, is prepared and used to decontaminate Chemical Warfare Agents (CWAs) simulants 2-CEES (2-chloroethyl ethyl sulfide) and DMMP (dimethyl methylphosphonate) in vapor phase. Compared with the unmodified pure TiO2 photocatalyst, the adsorption capacity on the sulfated photocatalyst increases by 50%, and the conversion for 2-CEES increases more than 20%. It is found that the durability for decontaminating DMMP is delayed by 200 min with the modified photocatalyst. The surface characteristics of the photocatalysts are analyzed by XPS and FT-IR. The results show that more Lewis and Bronsted acid sites, considered to be responsible for improving the reactivity performance of photocatalysts, are formed on the sulfated TiO2.