Aims and objectives. The aim of this study was to evaluate long-lasting changes in the nursing staff's understanding of oral health care for cancer patients after an oral health care intervention. The study also assessed whether there were changes between registered nurses and auxiliary nurses. Background. The maintenance of good oral health care in cancer patients is essential for nutrition, recovery and wellbeing and requires the involvement of nursing staff. However, several studies reveal that the need to prioritize oral health care has not been made sufficiently clear. Methods. The nursing staff (registered nurses, n = 133 and auxiliary nurses, n = 109) on five wards at different hospitals providing cancer care took part in a four-hour oral healthcare training session, including the use of an oral assessment guide and answered a questionnaire initially and after this intervention. The data were statistically analyzed. Results. Several aspects of implementation opportunities improved, but they did not include attitudes to oral health care. Knowledge of oral diseases decreased, more for auxiliary nurses than for registered nurses. Conclusions. A four-hour oral health training session and subsequent activities improve the nursing staff's understanding of oral health care for patients with cancer diagnoses in some respects but not in terms of attitudes to oral health care or specific oral knowledge. Relevance to clinical practice. Oral healthcare education and training activities for nursing staff can produce some improvements in the understanding of oral health care for cancer patients but not in attitudes and specific oral knowledge. These areas must be covered during the basic education period or/and by a routine oral healthcare programme for nursing staff, probably including an oral healthcare standard.