Cancers have an important place among the childhood health problems. Although deaths in childhood cancers have decreased in recent years, it has been reported that the incidence of cancer has increased. Although the incidence of childhood cancers is lower than that of adult cancers, 0.5% of all cancer cases are children under the age of 15. Treatments such as chemotherapy, radiotherapy, surgical treatment, and bone marrow transplantation are applied alone or in combination in cancer treatment. Chemotherapy, which is one of the most used treatment methods in childhood cancers, destroys cancer cells, can prevent the spread of cancer cells in the body and the recurrence of the disease by 60-70%. Chemotherapy can cause complications by affecting normal cells and tissues as well as cancer cells. Among these complications, anemia, alopecia, dermatitis, thrombocytopenia, mucositis, nausea-vomiting and pain are the most common complications. Oral mucositis is one of the most common complications after chemotherapy and is seen in approximately 52% to 80% of children receiving treatment. Oral mucositis can directly affect the individual's quality of life by causing major problems such as shedding of the oral mucosal skin, ulceration, bleeding, pain, bacterial, fungal and viral infections in sick individuals. These problems make it difficult for the child to eat, drink, swallow and speak, and may lead to the development of biopsychosocial problems such as changes in comfort, decrease in body image and self-esteem, and increase in hospitalization time and hospital cost. It is important to prevent and manage mucositis in order to increase the quality of life of these children and reduce their stress levels. Proper oral hygiene and care practices are effective in the prevention and management of mucositis. Oral care provided by nurses is very important. Nurses, who play a primary role in patient care, are responsible for oral care and the prevention of mucositis. In order to prevent the development of mucositis, nurses need to have sufficient knowledge and skills, comply with practice protocols, take part in research that will form the basis of evidence, and follow the results of these studies. The aim of basic oral care is to reduce the effect of oral microbial flora and to prevent opportunistic infections. Basic oral care; It consists of brushing teeth with a soft-bristled toothbrush, cleaning between teeth with dental floss, rinsing the mouth using sterile water, saline or sodium bicarbonate. In basic oral care, it is recommended that the platelet (PLT) number be above 50,000 mm3 and the white blood cell (WBC) count over 1,000 mm3 for brushing and flossing. There is insufficient evidence that any component of basic oral care in the evidence-based practice guidelines fully prevents oral mucositis. However, there is evidence that it reduces the severity and duration of oral mucositis. To prevent and treat mucositis, saline, sodium bicarbonate, granulocyte colony stimulating factor (G-CSF), granulocyte-macrophage colony stimulating factor (GM-CSF), zinc sulfate, cryotherapy, sucralfate suspension, amifostine, prostaglandi E2 (PGE2) ), hydroxypropyl cellulose film, mucous sealants such as polyvinylpyrrolidone/sodium hyaluronate, topical application of vitamins A and E, parenteral application of β-carotene, low-dose laser therapy, glutamine, royal jelly, honey, aloe vera solution, omega-3 fatty acid, andiroba oil, black mulberry molasses and black mulberry syrup are used. In his study in 2020, Chadayan used coconut oil in his oral care to heal oral mucositis, and it was found that rinsing the mouth with coconut oil reduced the degree of oral mucositis. Studies have found that coconut oil has an effect on plaque formation and plaque-related gingivitis. Coconut oil is an edible oil and is consumed as part of the staple diet in many tropical countries. Coconut oil differs from most other dietary fats in that the predominant composition of coconut oil is a medium-chain fatty acid, while the basic building blocks of most other oils are almost entirely long-chain fatty acids. This is the physical and affect its chemical properties. Coconut oil contains 92% saturated acids, about 50% of which is lauric acid. Breast milk is the only other naturally occurring substance that contains such a high concentration of lauric acid. Lauric acid has proven anti-inflammatory effects and antimicrobial effects. These include Candida species and various viruses, including Helicobacter pylori, Staphylococcus aureus, Escherichia vulneris, Enterobcater and Candida glabrata, Candida albicans, Candida stellatoidea, Candida parapsilosis, Candida tropicalis, and Candida krusei. This study was planned to determine the effect of oral care with coconut oil on the degree of oral mucositis in pediatric oncology patients.