The microstructure and electrical properties of Mn-Ni-Co-CuSi oxides negative temperature coefficient (NTC) thermistors were studied. The as-sintered (Mn1.62Ni0.72Co0.57-xCuxSi0.09)(4) (0 <= x <= 0.12) and (Mn1.2Ni0.78Co0.87-xCu0.15Six)O-4 (0 <= x <= 0.15) ceramics showed the solid solutions of Mn-Ni-Co-CuSi oxides with a cubic spinel structure. The addition of SiO2 led to an increase in the temperature coefficient of resistivity. This demonstrates that the SiO2 addition is desirable for developing highly sensitive NTC thermistors. In addition, the resistivity and the temperature coefficient of resistivity for (Mn1.62Ni0.72Co0.57-xCuxSi0.09)O-4 and (Mn1.2Ni0.78Co0.87-xCu0.15Six)O-4 NTC thermistors were controlled by changing the composition.