An investigation of the performances in Fischer-Tropsch reaction of 1 wt% M/WC(X) (M = Co, Ru; X=A, B), where A is a tungsten carbide protected by free carbon and B is a clean tungsten carbide, was carried out. Supported catalysts performances were compared to those of the parent tungsten carbides at 473K and 20 bar. It was found that WC(A) produces mainly hydrocarbons but also 20–40% alcohols, whereas WC(B) activity is only towards linear alkanes. Before catalytic test, a reduction in pure hydrogen allows obtaining Co0 and Ru0 dispersed on layers of free carbon covering the WC core for the WC(A), and on a surface free of oxygen for WC(B). Co as Ru dispersions are improved on WC(B) compared to WC(A). A direct consequence is that Co/WC(B) has a better activity than Co/WC(A). Ru–W alloy formation could be responsible of the inobservance of a better activity for Ru/WC(B). On contrary, addition of Ru on WC(A) highly increases the activity and the production of heavy hydrocarbons. This beneficial effect, not observed with cobalt, could be attributed to a better dispersion of ruthenium on a carbon polymeric surface of WC. © 2006 Elsevier B.V. All rights reserved.