Oral mucositis is reported to occurs in 40% of cancer patients on chemotherapy, suggesting the need for early oral care intervention in such patients. However, the oral care depends on each nurse and there has been no special document on the oral care for patients in the Respiratory Medicine and the Hematology/Oncology Ward, in which are managed around 100 regimens of chemotherapy per month. Here, to develop an oral care assessment sheet (OC sheet), we conducted a questionnaire survey of 24 ward nurses on oral care for chemotherapy patients and evaluated their assessment abilities using an oral care assessment test that was compliant with the items of the Eiler’s Oral Assessment Guide. The questionnaire survey revealed that nurses performed certain observations and/or interventions without basis and confidence, and that they did not always have patients’ cooperation while assessing their oral condition. They also tended to give inconsistent instructions. Use of the OC sheet enabled nurses to provide early oral care interventions and to confirm the utility of the chosen intervention. Test scores after the introduction of the OC sheet were significantly higher than before, indicating that use of the OC sheet improved nurses’ assessment and nursing care abilities.