Nanomaterial applications are a fast-developing field. In spite of their powerful advantages, many open questions regarding how these small-sized chemicals may influence the environment and human health. However, scarce reports are available on the potential hazards of combined nanoparticles, taken into consideration that nickel oxide (NiO) and cobalt (II, III) oxide (Co 3 O 4 ) nanoparticles (NPs) are already used together in many applications. Hence, the present work was designed to study the probable changes in some biological, hematological, and serum biochemical variables throughout 2 weeks following an oral administration of 0.5 g and 1.0 g of NiO-NPs or/and Co 3 O 4 -NPs per kilogram body weight of rats. As compared with the controls, the exposure to NiO-NPs or Co 3 O 4 -NPs solely caused significant elevations in the relative weights of brain (RBW), kidney (RKW) and liver (RLW), water consumption (WC), red blood cells (RBCs) count, hemoglobin (Hb) content, packed cell volume (PCV), and serum levels of low-density lipoprotein cholesterol (LDL-C), glucose, creatinine, urea, and uric acid as well as serum activities of aspartate and alanine aminotransferases (ASAT and ALAT). In addition, remarkable declines in the total body weight (TBW), feed consumption (FC), white blood cells (WBCs) count, serum levels of total protein (TP), albumin, albumin/globulin ratio, total cholesterol (TC), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C) were caused by administration of NiO-NPs or Co 3 O 4 -NPs, separately. On contrary, the co-administration of NiO-NPs and Co 3 O 4 -NPs together caused less noticeable changes in most of studied variables as compared with those administered NiO-NPs or Co 3 O 4 -NPs, individually. In conclusion, the exposure to a combination of NiO-NPs and Co 3 O 4 -NPs suppressed the adverse effects of the individual NPs on the studied variables.