Histone acetylation is one of the posttranslational modification that plays a role in the regulation of gene expression, also modulation of acetylation with histone deacetylase inhibitors (HDACi) had been considered a novel strategy for cancer chemoprevention. This study was aimed to investigate the activity of histone deacetylase enzyme (HDAC) in tumor cell model Solid Ehrlich carcinoma under the effect of the antitumor drug methotrexate in combination with sulforaphane (SFN) which is a natural compound found in cruciferous vegetables. In the present study, sulforaphane was extracted from cabbage outer leaves. The HDAC activity significantly increased in tumor-bearing mice, non-significantly decreased after treatment with methotrexate, and significantly decreased after treatment with methotrexate with oral supplement by sulforaphane. However, The DNA damage decreased significantly in tumor tissue of tumor-bearing mice after treatment with methotrexate and increased significantly in tumor tissue of tumor-bearing mice treated with oral sulforaphane in combination with methotrexate treatment after carcinogenesis. In conclusion, sulforaphane has an antitumor effect via its pro-oxidant activity and affects the HDAC activity via its metabolites in an inhibitory manner that enhanced the effect of methotrexate.