Enhancing the immune response while minimizing cancer-related damage is crucial for improving treatment outcomes in cancer therapy. We recently reported that chitosan nanoparticles (CNPs) could improve Sorafenib therapeutic potential and reduce EAC-triggered hepatic damage. This study aimed to investigate the immunomodulatory effects of CNPs on mice bearing Ehrlich ascites carcinoma (EAC) and evaluate their potential to alleviate EAC-induced spleen injury. A total of 21 female Swiss albino mice were randomly divided into 3 groups (7 mice per group): Group I (normal control) orally received PBS; Group II (EAC) was injected intraperitoneally with a single dose of 1 million EAC cells; and Group III (CNPs) consisted of EAC mice treated orally with CNPs from Day 4 to Day 14. Oxidative/antioxidant status was measured spectrophotometrically, CD4+ and CD8+ cell populations in the spleen were assessed by flow cytometry, and gene expression was analyzed through real-time polymerase chain reaction (qPCR). CNP treatment stimulated an immune response in EAC-bearing mice, as evidenced by increased globulin level, a higher count of CD4 and CD8 expressing cells, and enriched lymphocytes in the spleen. CNPs also restored oxidative balance, indicated by lower MDA levels and increased SOD, CAT, and GPx activities. Additionally, they reduced apoptosis (downregulation of Bax and upregulation of Bcl2), and decreased inflammation (downregulation of IL1β and TNFα) in the spleen. These findings suggest that CNPs not only restored spleen structure and function but also exhibited significant immunomodulatory effects in EAC-bearing mice.