The ferro-paramagnetic phase transition in dilute manganese-nickel base alloys is investigated through a qualitative study of their thermal conductivity as a function of temperature in the phase transition region. A (V-0) relation is applied to measure the ratio between thermal and electrical conductivity of two samples having Mn concentration: 1.17 at. % and 1.82 at. %. The thermal conductivity results were evaluated using the electrical resistivity data obtained for the same samples, but from a separate experiment. The results are compared with previous measurements on pure Ni and Fe, and their alloys. The validity of the Wiedmann-Franz law in the vicinity of the transition is examined.