Objective: Sulfur mustard is a chemical that causes the most damage in the war has had on the Warriors. Including the adverse effects of sulfur mustard is damage to the immune system. One of the drugs effective against thhese lesions is Acetylcysteine. Spleen has responsible part of the body’s immune system. Present study is about the effect Acetylcysteine for preventing damage in spleen tissue. Materials and Methods: Twenty one adult male rats were used to perform this study. Animals were randomly divided into three groups consist of solvent (saline), SM with dose 0.25 Percent and treated group with Acetylcysteine. Animals under anesthesia, received normal saline solution and SM received by intratracheal injection. Treated group received drug for fourteen days intraperitoneally. Animals were sacrificed in the end of 14th day of studying with ether. Sections have prapared from rat’s spleen. The sections were studied for histomorphology evaluation. To study the photographs of samples produced different microscopic magnification and percentage area of white pulp and germinal center were measured by the hardware and software Motic system. Statistical analysis was performed by ANOVA using Spss software. Data are reported as mean ± SEM at a significance level of p<0.05. Results: Our observations showed histomorphometrical average percentage of white pulp area of optical microscope with a magnification 100 in SM group compared to vehicle group was reduced but was not significant. This variable in treated group was greater than SM group and less than vehicle group. Average percentage of germinal center of white pulp in SM group was more than vehicle group but not significant this increasing was not seen in treated group. Conclusion: The use of Acetylcysteine could prevent inflammation in the spleen and immune system suppression.