Lung carcinogenesis is one of the main sources of cancer-related mortality globally and it is estimated that nearly 1 million people die from it every year. The 5-year survival rate of lung carcinogenesis is reported at just 15%. The aim of the current research was to investigate the immunomodulatory effect of eriocitrin against benzo(a)pyrene [B(a) P]-induced lung tumorigenesis in Swiss albino mice. The lung sarcoma was provoked through oral gavage of B(a)P (50 mg/kg body weight) two times/week for four weeks. CEA, lung weight, lipid peroxidation (LPO), body weight, immuno-globulin (IgG, IgA, and IgM), tumor incidence, serum marker enzymes (LDH, AHH, λ-GT, and 5'-NTs), hematological counts (leucocytes, lymphocytes, neutrophils, absolute numbers of lymphocytes and neutrophils), antioxidants (SOD and CAT), inflammatory modulators (IL-1β, IL-6, and TNF-α), immune complexes (avidity index, phagocyte index, NBT reduction, and SIC) and histopathological changes were analyzed. Moreover, the status of apoptosis proteins (Bax, caspase-9, and caspase-3) and cell proliferative protein (cyclin D1 and cyclin A) expression was determined by Western blot and PCNA by immunohistochemical analysis. B(a)P-challenged cancer-bearing mice exhibited augmented levels of lipid peroxidation, tumor incidence, lung weight, CEA, serum marker enzymes, IgA, SIC, cell proliferative markers, and inflammatory cytokines with concurrent decrease in body weight, antioxidant levels, hematological counts, immunoglobulins, immune complexes, and apoptotic protein expression. The eriocitrin treatments caused significant reversion of all these marker to previous levels. Overall, the results propose the immunomodulatory prospective of eriocitrin against B(a) P-induced lung carcinogenesis on Swiss albino mice.