Background: Oral mucositis often affects the quality of life of patients living with Chronic Obstructive Pulmonary Disease (COPD). Its symptoms include loss of oral mucous membranes, ulceration, bleeding and pain as well as bacterial, fungal and viral infections of the oral mucosa., Objectives: This study was carried out to investigate the effect of oral care with black mulberry syrup on oral mucositis healing in patients with COPD., Design: This mixed study was carried out in two stages- quantitative and qualitative. The quantitative stage was conducted as a randomized controlled experimental study while the qualitative stage was conducted by in-depth interview method., Setting: This study was conducted at the chest diseases clinic of a tertiary hospital in Turkey., Participants: The randomized controlled experimental study was completed with a total of 40 patients who had been diagnosed with COPD and oral mucositis between March 2017 and June 2018. They were divided into intervention and control groups consisting of 20 patients each. The qualitative study was conducted on 10 patients in the intervention group., Intervention: Patients in the intervention group gargled with 5 ml of black mulberry syrup for an average of 1 minute and swallowed it upon completion. They did this 3 times a day after meals for a period of 15 days after which they were interviewed., Outcome Measures: The quantitative data was collected using the Patient Information Form, Oral Evaluation Guideline, and WHO Oral Mucositis Scoring Index, while the qualitative data was collected using the in-depth interview form. Patients' oral mucosa was assessed a total of 3 times during 3 interviews held on the first, seventh and fifteenth days of the study., Results: There was a significant decrease in scores of oral mucositis of the patients in the intervention group at the second and third follow-ups. Oral mucositis of the intervention and the control groups healed at an average of 9.1 ± 2.5 days and 12.1 ± 1.4 days, respectively. In addition, oral care with black mulberry syrup was found to alleviate mucositis-related symptoms., Conclusion: Oral care with black mulberry syrup accelerates mucositis healing and alleviates mucositis-related symptoms.