Introduction: Conflict reports exist on the impact of pyrethroid insecticides on immune function and the probable underlying mechanisms.Methods: This study evaluated the effect of an extensively used pyrethroid insecticide, fenpropathrin (FTN) (15 mg/kg b.wt), on the innate and humoral immune components, blood cells, splenic oxidative status, and mRNA expression of CD3, CD20, CD56, CD8, CD4, IL-6, TNF-α, and Caspase3 in a 60-day trial in rats. Besides, the possible defensive effect of curcumin-loaded chitosan nanoparticle (CML-CNP) (50 mg/kg b.wt) was evaluated.Results: FTN exposure resulted in hypochromic normocytic anemia, thrombocytosis, leukocytosis, and lymphopenia. Besides, a significant reduction in IgG, not IgM, but increased C3 serum levels was evident in the FTN-exposed rats. Moreover, their splenic tissues displayed a substantial increase in the ROS, MDA, IL-6, and IL-1β content, altered splenic histology, and reduced GPX, GSH, and GSH/GSSG. Furthermore, a substantial upregulation of mRNA expression of splenic CD20, CD56, CD8, CD4, CD3, IL-6, and TNF-α, but downregulation of CD8 was detected in FTN-exposed rats. FTN exposure significantly upregulated splenic Caspase-3 and increased its immunohistochemical expression, along with elevated TNF-α immunoexpression. However, the alterations in immune function, splenic antioxidant status, blood cell populations, and immune-related gene expression were notably restored in the FTN + CML-CNP-treated group.Conclusion: The findings of this study highlighted the immunosuppressive effects of FTN and suggested the involvement of many CD cell markers as a potential underlying mechanism. Additionally, the results demonstrated the effectiveness of CML-CNP in mitigating pollutant-induced immune disorders.