The deposition of RuO2 thin films by plasma-enhanced chemical vapor deposition (PECVD) with ruthenocene as a precursor has been investigated with various ratios of precursor/oxygen at the substrate temperature of 500 degrees C. When an Ru + RuO2 mixture was deposited by thermal CVD, RuO2 thin films of minimum resistivity of about 55 mu Omega cm were successfully deposited by PECVD under the same conditions. It is found that there is a strong tendency to RuO2 formation as the ratio of precursor/oxygen is decreased. It is concluded that nut only the amount of activated oxygen atoms but also the ratio of precursor/oxygen is important for RuO2 formation.