Nickel oxide (NiO) and cobalt (II, III) oxide (Co₃O₄) nanoparticles (NPs) are widely used together in alloys and as catalyzers. Yet, no information is available about the effect of their combination on mammals. The present work investigated the accumulation and the toxicokinetics of Ni and Co in the brain, liver, kidney and intestine of male albino rats during two weeks after an oral administration of 0.5 and 1.0 g per kg body weight of NiO-NPs and/or Co₃O₄-NPs. Characterization of the NPs via transmission electron microscope (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS) was performed. The average particle diameter, hydrodynamic size, polydispersion index and zeta potential were 16.90 nm, 91.54 nm, 0.394 and + 42.1 mV for the NiO-NPs and 20.68 nm, 92.03 nm, 0.235 and +41.5 mV for the Co₃O₄-NPs, respectively. In all tissues, Ni levels were markedly increased with increasing the administered doses of NiO-NPs. On the contrary, Co levels were remarkably reduced by elevating the doses of Co₃O₄-NPs. The highest levels of Ni and Co were reported in the intestine. The toxicokinetic parameters including the area under concentration curve (AUC), maximum concentration (C_max), elimination rate constant (Lz), elimination half life time (t_1/2), mean retention time (MRT) and last recorded concentrations (C_last) of Ni and Co were computed in all the studied organs. The rats administered with NiO-NPs and Co₃O₄-NPs together showed remarkable reductions in the AUC and C_max of Ni and Co, as compared to those treated with either NiO-NPs or Co₃O₄-NPs separately. A marked increase in the Lz accompanied by remarkable reductions in the t_1/2 and MRT of Ni in the kidney of rats administered with NiO-NPs and Co₃O₄-NPs together, as compared to those treated with NiO-NPs alone. Accordingly, the co-administration of NiO-NPs and Co₃O₄-NPs markedly reduced the absorption of the Ni and Co, whereas it increased their elimination rates. In conclusion, under the current experimental conditions, the NiO-NPs and Co₃O₄-NPs antagonized each other inside the body.