Pneumonia is one of the most important diseases in terms of mortality in the elderly. In particular, bedridden patients who are forbidden oral ingestion during enteral nutrition may have a poor outcome resulting from a respiratory infection. Oral hygiene can play a positive role in preventing aspiration pneumonia in the elderly. The aim of this study was to investigate the effectiveness of oral hygiene for bedridden and tube-fed patients at an increased risk of pneumonia. This retrospective study was conducted from July 2011 to June 2013 on a long-term-care hospital unit. The oral care protocol (OCP) intervention commenced in July 2012, during the study period. The subjects of this study were 63 elderly patients with a mean age of 81.7 years. Thirty-one patients were enrolled in the OCP intervention group, and the mean observation length was 130.4 days; the mean observation length for the 32 patients in the control group was 128.4 days. The incidence of pneumonia and the numbers of days with a recorded fever, antibiotics administration, blood tests, and radiological examinations were reduced from 1.20 to 0.45, 24.57 to 17.48, 25.52 to 10.12, 10.91 to 6.54, and 6.33 to 3.09 %, respectively. These reductions were significantly less in the OCP intervention group. In conclusion, the results of the present study suggest that daily oral care for tube-fed patients who do not receive nutrition by mouth reduced the incidence of pneumonia. In addition to patients consuming food by mouth, all tube-fed patients require dedicated oral care to maintain healthy oral conditions.