Zinc oxide nanoparticles (ZnO-NPs) are widely used in the food and fertilizer industries. During our previous study, the bean fertilized by two doses (20 and 40 ppm) of ZnO-NPs with a particle size of 20 nm was investigated on rats. Therefore, this experiment was designed to evaluate effect of ZnO-NPs that were administrated orally to rats once a day at the doses 20 and 40 ppm. Hematological and biochemical parameters were quantified in addition to investigation of the deleterious effect on liver and kidney histopathological. In-vitro cytotoxicity of ZnO-NPs on the Vero cell line was also studied. Eighteen male Wistar rats were divided into three groups. Normal control (G1) was administered deionized water (1ml/rat). Groups G2 and G3 received 1ml/rat suspensions of 20 and 40 ppm ZnO-NPs, respectively. Hematology showed that the mean corpuscular hemoglobin concentration (MCHC) was lower in G2 and G3. White blood cell count was decreased in G2. G3 had an elevated hematocrit. In G2 and G3, plasma glucose decreased while uric acid and alkaline phosphatase activity increased. Plasma creatinine, aspartate aminotransferase, alanine aminotransferase, and creatine kinase were all elevated in G3, while albumin levels were decreased. Treatment with ZnO-NPs for 72 h resulted in no toxicity in Vero cells when compared to normal ZnO. Biochemical data were confirmed by histopathology. In conclusion, both doses of ZnO-NPs had minimal effects on the hematological parameters. While 40 ppm ZnO-NPs should be applied carefully due to their negative effects on liver and kidney functions.