In this work, the structure and electrochemical properties of PtRu/C electrocatalysts obtained via the formation of a sulfide complex method and submitted to thermal treatment in reducing environments are discussed. It is seen that for the non-treated material, the Ru atoms are segregated from the Pt fcc structure, probably forming an amorphous ruthenium oxide phase, while for PtRu/C heat treated at 700 degreesC under hydrogen atmosphere there is the formation of a true alloy with a metal Pt:Ru composition of ca. 3:1. It is also seen that the Pt atoms present more vacant 5d electronic states in the PtRu/C dispersed catalysts, an effect related to the electron withdrawing property of Ru. Due to the low degree of PtRu alloying, the performance of the as prepared PtRu/C catalyst for the hydrogen oxidation reaction in the presence of 100 ppm CO is very poor. However, an important improvement is observed when the catalyst structure is modified by increasing the heat treatment temperature. Here, despite the reduction on the active surface area, the best CO tolerance is achieved for ca. 3:1 Pt:Ru alloy real proportion.