Background: To evaluate, in an initial way, the effectiveness of bioadhesive chlorhexidine gel 0.2% versus placebo as a preventive and therapeutic intervention of oral mucositis induced by radiation therapy and chemotherapy in patients diagnosed with head and neck cancer treated with chemoradiotherapy. Material and Methods: In this pilot study, 7 patients (range of age: 18- 65), having histological documented diagnosis of squamous carcinoma on the head and neck region in stage III and IV, and receiving combined radiation treatment and chemotherapy (cisplatin 100 mg/m2 IV on days 1, 22, and 43 of irradiation) were studied. Simultaneously, a topical application was performed with bioadhesive chlorhexidine gel 0.2% in the study group, and the placebo gel for the control group in 5 applications per day, from the time of initiation of cancer treatment to 2 weeks after completion of chemo-radiotherapy treatment (11 weeks of follow-up). The gradation of mucositis, pain, analgesic consumption, infectious complications, and treatment tolerance was measured. Results: After 7 patients completed the protocol, any differences were observed between groups in an interval analysis. Mucositis, pain, and tolerance was similar in both groups. Conclusions: Our results must be interpreted with caution due to the reduced sample size, but the use of bioadhesive chlorhexidine gel 0.2% didn’t contribute clinical improvement to the oral mucositis induced by radiation therapy and chemotherapy.