This study was carried out to determine the therapeutic effect of Nigelle saliva oil extract on mice experimentally infected with Cryptos­poridium parvum. For this purpose. 25 susceptible swiss mice (2-3 weeks old) were divided into 3 groups. Group I included infected 11 treated mice, group II included 10 infected non-treated ones, and group III composed of 4 non-infected non-treated mice. One week before ex­perimental infection, all mice were immunosupressed by a mixture of 2 mg/t. dexamethasone sodium phosphate and SOO mg/L tetracycline hy­drochloride In daily fresh drinking water. Experimental infection of mice was carried out with cryptospoddium pawum oocysts isolated from natu­rally infected calves. One week later, mice of group I were orally treated with Nigelle oil at a dose of 1 m1/100g body weight for each mouse. Fae­cal pellets from rectum of each mouse in all groups were examined every other day post-treatment by the Modified Ziehl-Neelsen technique. 0e-cysts intensities were scored in 100 randomly selected fields. The results revealed that mice of group III were refractory, while, mice of group I showed a reduction in oocysts count when compared to those of group II. On day 35th, all mice were sacrificed and parts of their ilea were fixed in 10% formalin solution for histopathotogical examina­tion, as well as, smears from ilea were taken and stained with the Modi­fied Ziehl-Neelsen technique. Villi of ileum of mice in group I showed nor­mal appearance without any changes, while, those of mice of group II showed apparent villus atrophy: shortening and blunting with desquama­tion of most of villi. Villi of group III were normal. Data were statistically analysed and discussed.