Tumor hypoxia adversely affects clinical radiation response of head and neck squamous cell carcinoma. 18F-fluoromisonidazole positron emission tomography ([F-18]FMISO-PET) offers a noninvasive means of assessing viable hypoxic tissue in tumor. We evaluate hypoxia imaging with [F-18]FMISO-PET in HNSCC treated with chemoradiotherapy. A total of 11 patients with HNSCC agreed to participate in this study. All of the patients underwent pretreatment [F-18]FMISO-PET. SUVmax and tumor-to-muscle ratios(TMR) were measured as hypoxia indicators. 9 patients of them had primary tumor hypoxia. 2 of 10 patients with neck metastasis had nodal hypoxia. All patients were treated with chemoradiation therapy. As clinical response of chemoradiotherapy, 8 patients achieved CR, 3 patients achieved PR. Remain viable carcinoma cell of 3 PR cases existed in hypoxia region imaged with [F-18]FMISO-PET. The current result suggest that we could apply 18-F fluoromisonidazole positron emission tomography/computed tomography ([F-18]FMISO-PET/CT)-guided intensity-modulated radiotherapy(IMRT) in dose escalation to attack the hypoxic volume of a tumor mass without increasing the normal tissue dose in head and neck cancer patients in order to improve the clinical response.