Oral Mucositis refers to oral mucosa erythematous and ulcerative lesions and is caused by radiation dispensed in the treatment of malignant tumors of the head and neck. Propolis shows several biological activities such as antimicrobial and anti-inflammatory properties. These biological activities should prevent a mucositis. The aim is to verify the effectiveness of Brazilian green propolis in a mucoadhesive gel, alcohol free, in preventing oral mucositis in patients that underwent radiotherapy. This research is characterized as a preliminary study with a mean duration of 12 weeks of patients' follow-up in two groups. The selection of participant's groups was randomized. The 26 selected patients were distributed between two groups, 13 in the benzydamine group and 13 in the propolis group. Patients were assessed on an average of 4.5 times totaling 116 diagnoses of mucositis. The percentage of patients who had mucositis greater or equal to 2 in this study was 30.6% for the benzydamine group and 29.6% for propolis gel. For these patients, the propolis gel shows a better performance in maintaining lower rates/grades and recovery of patients from the 17 th session of radiotherapy. This work shows a great possibility of further study in Phase III due to its good results and acceptance with patients.