Introduction: Globally, breast cancer is the second most prevalent cancer among women and its incidence is amplifying alarmingly. Since genetic factors is believed to account for only 10% of the reported cases, remaining the environmental factors including diet are thought to play a significant role in predisposing breast cancer. Many bioactive compounds have been reported for their anticancer potential. One among the bioactive compound is 3,30 - diindolylmethane (DIM) is a phytochemical possess a wide array of pharmacological activities such as anti-proliferative and antioxidant properties. Its properties such as poor water solubility and low bioavailability have hampered its clinical development. Therefore, it is a great interest to study whether the nano formulation for DIM with chitosan for an enhanced their potential, the present study was aimed to evaluate the chemotherapeutic potential of 3,30 -diindolylmethane (DIM) encapsulated chitosan nanoparticles (DIM@CS-NP) on 7,12-dimetheyl benz(a)anthracene (DMBA) induced mammary carcinoma in female Sprague Dawley rats