The tribological behaviour of HVOF-sprayed Co-28%Mo-17%Cr-3%Si coatings, both in the as-sprayed condition and after thermal treatments at 200°C, 400°C, 600°C for 1h, has been studied. Microstructural and micromechanical properties were characterized by SEM, XRD, Vickers microhardness and indentation fracture toughness; dry sliding wear tests are performed by pin-on-disk equipment against 100Cr6 and sintered alumina pins. The as-sprayed coating contains splat boundary oxide stringers and is mostly amorphous (splat quenching). It possesses low hardness (~6.7GPa) and toughness (~1MPa*m^1/2); thus, much adhesive wear occurs against 100Cr6 steel. The friction coefficient increases up to ~0.9, raising the contact point temperature up to a critical oxidation value for the coating; then, it decreases, increases agains and finally settles at a stable value. Much of the adhesive wear occurs in the first stage of the test. Abrasive wear prevails with the alumina pin: the coating wear rate is lower because the metallic alloy possesses intrinsically good plasticity. Adhesive phenomena still occur, leading to the same thermal effects. After the 200°C and 400°C heat treatments, no major changes occur. The 600°C treatment causes the formation of some submicrometric crystals. The hardness is increased (~8.8GPa), adhesion to 100Cr6 steel is prevented and the friction coefficient soon settles at ~0.8 with no peaks. The coating undergoes no wear loss and the pin wear rate is largely decreased. With the alumina pin, coating and pin wear rates remain quite low. However, adhesion is reduced, so that the friction coefficient has no peaks and its final value is lowered (from 0.84 to 0.75).