The influence of the substitution of Co for Ru on the magnetic hyperfine fields Bhf on 119Sn nuclei in UCo1−xRuxSn solid solutions was investigated. The compounds were crystallized in a hexagonal crystal structure of the ZrNiAl type. This structure is characterized by two nonequivalent crystal positions of d-metal. It was shown that Bhf measured at 5 K decreases with an increase in Ru content. Such a dependence of Bhf is opposite to the concentration dependence of the uranium magnetic moments. Therefore, the different mechanisms and electron groups are responsible for the formation of the U magnetic moments and the hyperfine magnetic field on the 119Sn nuclei. It has been concluded from analysis of the obtained results that (i) the observed linear reduction of electron polarization on 119Sn nuclei can be explained by the decrease in density of the s-electrons due to the hybridization of the s-electrons of Sn with Ru/Co atoms, and (ii) the Ru/Co atoms in the two crystal positions make significantly different contributions not just to the 5f-d hybridized band but also to the formation of the magnetic hyperfine fields on 119Sn nuclei.