The D.C. electrical conductivity of nano-composite Si3N4-SiC films prepared by the plasma CVD method at 400-degrees-C was measured by the three-terminal technique. It was estimated that the electrical conduction in Si3N4 films was due to the hopping mechanism which gave the ohmic characteristics and Poole-Frenkel mechanism below and above the electric field of 9 x 10(6) V.M-1, respectively. The electrical conduction in SiN1.01C0.28 (abbreviated as 'SiNC') and SiC films was estimated to show the hopping mechanism under the whole field studied. The activation energies of coduction for Si3N4, SiNC and SiC films were approximately 0.72, 1.64 and 0.43 eV, respectively at about 130-degrees-C; the SiNC film showed an extremely high value. The activation energies of these films were much lower than the optical band gaps (2.7-5.3 eV). The electrical conduction in the compositional range froM Si3N4 to SiC at a constant temperature showed a maximum near the atomic ratio (C/Si) of 0.3 without obeying the theory of composite. This was assumed that the electrical conduction of the SiN(x)C(y) films was influenced by the difference in number of valence electrons between N and C and the structural change from Si3N4 to SiC since N and C atoms around Si were mixed uniformly on an atomic scale.