Objective: To evaluate xerostomia, mucositis and dental caries during head and neck radiotherapy. Methods: Twenty patients with nasopharyngeal carcinoma were included. Oral examinations were conducted before radiotherapy, after dosage of 2000 cGy irradiation, immediately after the termination of radiotherapy, and 1 month and 6 months after termination of the radiotherapy. Oral hygiene instruction, effective oral care and dental intervention were performed during the treatment. Salivary flow rate was evaluated by modified Schirmer's test. Xerostomia, mucositis and dental caries status were evaluated based on oral examinations. Results: Salivary flow rate decreased significantly after the first dosage of 2000 cGy, and was aggravated with the increase in irradiation dosage until the termination of radiotherapy. Xerostomia and mucositis were observed in parallel with the reduction of saliva flow rate, and were aggravated with the increase in irradiation dosage. Mucositis began to recover within 1 month after the termination of radiotherapy and fully recovered within 6 months after the termination of the radiotherapy. Six months after the termination of irradiation, new carious lesions were detected in two patients. Conclusion: Oral sequelae developed during radiotherapy of the head and neck. Oral health instructions and effective intervention were essential before, during and after the radiotherapy. Keywords: xerostomia, mucositis, dental caries