Background: Elevated Staphylococcus aureus and oral bacterial concentrations are known to correlate with pneumonia hospitalization in nursing home residents. However, the effects of a professional oral care intervention on these factors remain unclear. The aims of this quasi-experimental study were to compare bacterial concentrations in saliva and sputum, oral health status, distribution of Staphylococcus aureus, and pneumonia status before and after a professional oral care intervention. Methods: A purposive sample of residents from two nursing homes was divided into an intervention group that received a weekly professional oral care intervention and a control group. Oral bacterial concentration was determined by real-time polymerase chain reaction. The Staphylococcus aureus distribution was determined by bacterial culture and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. After data collection, a statistical analysis was performed to evaluate the effect of the intervention.