Metallic oxide nanoparticles are increasingly being incorporated into consumer products, posing health hazards and damage to the ecology when they are released into the environment. In view of this situation, the development of highly sensitive and facile methods for the detection and quantification of harmful metallic oxide nanoparticles present in a sample is necessary. In addition, it is important to be able to detect nanoparticles from their mixtures. Hence, in this preliminary work, the electrochemical behaviors of copper oxide/nickel oxide nanoparticle mixtures (CuO–NiO NP) in alkaline media have been studied to investigate the possibility of simultaneously determining two nanoparticles in a complex system. It was discovered that this technique could quantify the amount of copper oxide and nickel oxide nanoparticles in the range of 0.5–2.0 μg if the mass ratio of the copper oxide and nickel oxide nanoparticles in the mixture is one. However, if the ratio deviates from one, quantification becomes unreliable. More studies need to be carried out to investigate the reasons behind this phenomenon to allow for indiscriminant application of this technique in the future.