A new inverse microemulsion system containing a zwitterionic surfactant, cetyltrimethyl-ammonium p-toluene sulfonate, was used to prepare the nanoparticles of mixed transition-metal spinel oxide, CoFe2O4 and of single metal oxides of zinc, cadmium, and nickel (ZnO, CdO, NiO). The prepared cobalt ferrites had an average crystalline size of 20-40 nm, whereas the single metal oxides prepared in inverse microemulsions had an average crystalline size of 40-90 nm. All the prepared nanoparticles could be characterized using XRD and SEM methods.