Purpose: This study was performed to determine the relationship between oral-mucosal pressure ulcer (PU) stage and mechanical conditions and individual susceptibility in intubated patients. Methods: We collected 80 patient-days data from an intensive care unit of a 700-bed hospital in Korea. We analyzed oral-mucosal PUs, medical records, amount of saliva, and oral mucosal swabs. Bacterial abundance was enumerated by real-time polymerase chain reaction. The χ2 or Fisher’s exact test, t-test or Mann-Whitney U test, and Spearman’s rho correlation analysis were performed. Results: The incidence of overall oral-mucosal PUs was 31.3%, and in the maxillary and mandibular sites were 16.3% and 26.3%, respectively. There were significant correlations between the maxillary site PU stage and restraint use (r = .43, p < .001), albumin level (r = −.22, p = .046), and relative abundance of P. aeruginosa (r = .45, p < .001) and S. aureus (r = −.24, p = .033). In the mandibular sites, there were significant correlations between PU stage and restraint use (r = .30, p = .008), level of consciousness (r = .31, p = .005), and relative abundance of P. aeruginosa (r = .25, p = .028) and S. pneumoniae (r = .22, p = .046). Conclusions: Frequent monitoring and repositioning the mechanical pressure on the oral-mucosa could be an effective preventive strategy against the development and advancement of oral-mucosal PUs. Additionally, monitoring the oral microorganisms can prevent advanced stage oral-mucosal PUs in intubated patients.