Background: Cyclophosphamide (CYP) is an alkylating drug used in cancer treatment, one of its common complications is hemorrhagic cystitis (HC). Pumpkin seed oil (PSO) is a strong anti-inflammatory, antioxidant and anticancer. Aim of the Work: This study was carried out to study the possible protective effect of pumpkin seed oil on cyclophosphamide induced hemorrhagic cystitis. Materials & Methods: The present study was carried out on 45 adult male albino rats. They were randomly divided into four main groups. Group I represented the control group. Group ll (PSO) received PSO at a dose of (40mg/kg/day) orally for 28 days. Group lll (HC) received CYP solution (75 mg/kg) for induction of HC. Group IV (PSO+HC) received PSO for 28 days as in group II, and at the 20^th day, HC was induced by the same dose and manner as in group III. The urinary bladder specimens were processed for different histological techniques. Morphometrical and statistical studies were also performed. Results: Group III showed a lot of changes at the level of light microscopic study including epithelial ulceration, nuclear changes, hemorrhage, extensive fibrosis in Masson Trichrome stained sections and weak PAS reaction. Furthermore, HC group showed strong positive immune reaction in the Bax immunostained sections. These findings were confirmed in our morphometric data. Additionally, ultrastructural examination of HC group showed rarefied cytoplasm, widening of intercellular spaces and swollen mitochondria. Meanwhile, group IV showed marked improvement of the previously mentioned pathological changes. Conclusion: PSO administration plays a protective role in cyclophosphamide-induced hemorrhagic cystitis.