RuO x films were deposited by chemical vapor deposition with different oxygen flow rates on sputtered Ru film, and the annealing effects on the properties of the bi-layers were investigated. Films deposited with an oxygen flow rate of 800 sccm and less have the structure of hcp Ru, while a flow rate of O 2 of 1200 sccm and above results in RuO 2 films. The post-deposition thermal treatments were performed in N 2 (for 60 s and 30 min) and forming gas (for 30 min) ambients at the temperature range of 100-750 o C. In all films, resistivity decreases as the treatment temperature increases, and this behavior is independent of the treatment ambient and time. Rapid thermal annealing (RTA) in N 2 ambient or annealing in forming gas result in samples with low resistivity compared to N 2 flow furnace annealing; the higher resistivity of the latter case is attributed to oxidation from residual oxygen. Ru films prepared with 800 sccm O 2 flow become highly (001) textured after thermal treatment due to a re-crystallization process. The RuO 2 phase films develop cracks after forming gas annealing due to an oxygen reduction reaction. The RuO 2 phase changes to Ru after 750 o C RTA by the volatilization process. After RTA at 600 o C, the stress increases in all films due to the densification or/and phase change from RuO 2 to Ru.