Praziquantel, the commonly used anti--schistosomal drug, was investigated for hepatic carcinogenesis promoting potential using Diethylnitrosamine (DEN) - induced hepatic neoplasia in rats as a model in our study. Fity rats were given a daily dose of 5 mg/Kg body weight DEN in drinking water, for 12 weeks, while twenty rats were used as control groups. On the sixth week, preneoplastic changes have been developed. Out of these 50 rats, 20 rats were received praziquantel for 6 successive days at a dose of 30 mg/kg body weight, in addition to DEN administration. At the beginning of the experiment and at week 12 of the experiment, sera and blood samples were collected from all rats and examined. The average increase of the total immunoglobulins (Igs) in rats received DEN (324% + 64.45) is about 3 fold in comparison to the control group (100% + 32.5) This increase is reversed in rats receiving praziquantel (115% + 33. 35). Praziquantel alone has no effect in the total Igs (101% + 76.3). Additionally, the average of the total RBCs counts and the hematocrite value (PCV) were increased by DEN administration (14.35 + 1.96, 63.62 + 0.4 respectively), in comparison to the control group (7.6 + 0.36, 46.6 + 0.72). The effect was reversed by praziquantel (9.45 + 1.05, 40 + 7). However, praziquantel alone has no effect (7.36 + 0.20, 38.37 + 0.11). On the other hand, DEN adminsitration increases hemoglobin (HB) concentration with average (21.33 + 0.47), in comparison to the control group (16.2 + 1.2). LA However, this effect could not be reversed by praziquantel (21 + 4.49), nor could be produced by praziquantel (14.28 + 1.18). There is no significant changes in the average counts of WBCs or the differential counts in all groups of rats. The mechanism of action DEN and praziquantal on both the immunological and hematological changes was discussed.