The carbon-nickel nanocomposite thin films (C-Ni films) were deposited on n-type silicon (n-Si) wafers using reactive sputtering from a pure nickel target in methane/argon sputtering gas. Six kinds of C-Ni films were prepared with the rf power being 50, 100, 150, 200, 250, and 300 W, and the effect of different rf powers on the characteristics of C-Ni films is studied. The measured results show that the carbon-hydrogen bonds in C-Ni films decrease with increasing the rf power from 50 to 100 W, but no carbon-hydrogen bonds were found in C-Ni films with the rf power above 150 W. When the rf power increases from 50 to 300 W, the Ni/C ratio in C-Ni films increases from 0.2 to 55.8% and the sp(2)/(sp(2) + sp(3)) carbon ratio in C-Ni films also increases from 40 to 84%. Additionally, the degree of crystallinity of C-Ni films increases with increasing the rf power from 50 to 300 W, and the structure of C-Ni films changes from amorphous carbons to containing an amount of rhombohedral Ni3C compounds. The Ni/C ratio and degree of graphitization of C-Ni films increase with increasing the rf power from 50 to 300 W, so the optical band gap of C-Ni films decreases from 2 to 0 eV and the electrical resistivity of C-Ni films decreases from 3.6x10(4) to 8.6 x 10(-5) Omega.m. The current density-voltage behavior displays that the C-Ni/n- Si device has the rectifying characteristic. As the C-Ni film was prepared at the rf power of 150 W, the C-Ni/nSi device has the best ideality factor of 2.6. One can predict that the C-Ni/n-Si device has the potential to be applied in the electronic/optoelectronic fields.