Objectives: Recently, increased attention has been given to pumpkin due to its proved nutritional components, which include antioxidant, antifatigue, and anti-inflammatory effects. The aim of the present work was to assess the impact of Cucurbita pepo L. (CP) on chronic unpredictable mild stress (CUMS)-induced changes in lymphoid organs through evaluating its effect on the histological structure of spleen, thymus gland, and lymph nodes compared to the antidepressant fluoxetine (FLU). Materials and Methods: Fifty male albino rats equally distributed into five groups that included control, control + CP, CUMS-exposed, FLU-treated, and CP-treated groups were used in this study. Rats were exposed to CUMS for 4 weeks, and treatment (either with FLU or CP) was started after 14 days of exposure. Behavior of the rats, serum corticosterone, oxidants/antioxidants profile, proinflammatory cytokines, and gene expression of glucocorticoid receptor (GR) and β-adrenergic receptor (β2-AR) were assessed after 28 days. Spleen, thymus gland, and lymph nodes were histopathologically assessed. Results: CP administration significantly reduced the CUMS-induced behavioural changes evident by the significant reduction in immobility time (p = 0.02) and corticosterone level (p < 0.001). Biochemically, CP reduced TNF-α and IL-6 (p < 0.001) and markedly alleviated the changes in oxidants/antioxidants in the serum and lymphoid organs compared to fluoxetine. CP significantly (p < 0.001) reduced CUMS-induced changes in GR and (β2-AR). Histopathologically, CP alleviated changes observed in the spleen, lymph nodes, and thymus gland. It significantly reduced the number of CD4, CD8, CD68, CD20, and caspase-3 immunopositive cells in the studied organs. Conclusions: This study proved the potential efficacy of CP in alleviating depression-associated immunodysregulation either alone or in combination with antidepressant therapy.