This study was designed to determine the effect of the treatment schedule on the interaction between docetaxel and irradiation. Human head and neck squamous cell carcinoma (HNSCC) cells with different p53 status, and HSC4 (p53 wild-type) and CAL27 (p53 mutant type) cells were treated with docetaxel and irradiation using three schedules: i) concurrent treatment, ii) docetaxel pretreatment and iii) pre-radiation. Docetaxel and radiation inhibited the proliferation of HSC4 and CAL27 cells in a dose-dependent manner. However, irradiation pretreatment was more effective than the other treatment regimens in all cells. Our data suggest that pre-radiation in HNSCC cells significantly enhances docetaxel cytotoxity by arresting S-phase, and this provides the most effective treatment sequence of docetaxel and radiation combination therapy. Therefore, radiation followed by docetaxel may be the most effective sequence for head and neck cancer therapy.