The isotopic yields of Ru-105-111 in the C-12 and F-19-induced fission of U-233, U-235, U-238 and Np-237 have been measured using a fast radiochemical separation technique followed by gamma-ray spectrometry. The results show that the isotopic distribution consists of two components, i.e. neutron-deficient region and neutron-rich one. The formation of the neutron-deficient isotopes is mainly attributed to the complete fusion-fission reaction. For the neutron-rich Ru isotopes, the incomplete fusion-fission (peripheral interaction) contributes to their formation. The ratio of the yield in the neutron-rich region to that in the neutron-deficient region is determined by Gaussian fit of the isotopic distribution.