Background and objectives: Oral mucositis is one of the main adverse events of cancer treatment with chemotherapy or radiation therapy. It presents as erythema, atrophy or/and ulceration of oral mucosa. It occurs in almost all patients, who receive radiation therapy of the head and neck area and from 20% to 80% of patients who receive chemotherapy. There are few clinical trials in the literature proving any kind of treatment or prevention methods to be effective. Therefore, the aim of this study is to perform systematic review of literature and examine the most effective treatment and prevention methods for chemotherapy or/and radiotherapy induced oral mucositis. Materials and methods: Clinical human trials, published from 1 January 2007 to 31 December 2017 in English, were included in this systematic review of literature. Preferred reporting items for systematic reviews and meta-analysis (PRISMA) protocol was followed while planning, providing objectives, selecting studies and analyzing data for this systematic review. “MEDLINE” and “PubMed Central” databases were used to search eligible clinical trials. Clinical trials researching medication, oral hygiene, cryotherapy or laser therapy efficiency in treatment or/and prevention of oral mucositis were included in this systematic review. Results: Results of the studies used in this systematic review of literature showed that laser therapy, cryotherapy, professional oral hygiene, antimicrobial agents, Royal jelly, L. brevis lozenges, Zync supplementation and Benzydamine are the best treatment or/and prevention methods for oral mucositis. Conclusions: Palifermin, Chlorhexidine, Smecta, Actovegin, Kangfuxin, L. brevis lozenges, Royal jelly, Zync supplement, Benzydamine, cryotherapy, laser therapy and professional oral hygiene may be used in oral mucositis treatment and prevention.