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Oral candidiasis is the most common opportunistic fungal infection in patients undergoing head and neck radiotherapy (RT). The present study is aimed at provide the best treatment for patients undergoing RT by determining the characteristics of the Candida species in these patients and investigating the antifungal sensitivity patterns against eight available drugs according to the Clinical and Laboratory Standards Institute (CLSI). In this descriptive cross-sectional study, 30 patients underwent head and neck RT. All patients were examined in three stages using oral and pharyngeal mucus swabs, and nystatin was prescribed for patients with symptoms of candidiasis infection. Subsequently, clinical fungal specimens were investigated by direct microscopy and culture and tested for sensitivity to antifungal drugs. MIC₅₀, MIC₉₀, and geometric mean MIC were calculated for each drug. Evidence of fungal colonization was observed in 17 specimens at various stages, with Candida albicans being the most frequently identified species. All tested Candida isolates were sensitive to nystatin and amphotericin B, whereas Trichosporon asahii showed intrinsic resistance to echinocandins (caspofungin, anidulafungin, and micafungin), and C. krusei exhibited the expected intrinsic resistance to fluconazole. The observed sensitivity of C. tropicalis to the tested antifungal drugs is based on a single isolate and should be considered descriptive rather than generalizable. Cases of C. albicans strains showed moderate or dose-dependent susceptibility to itraconazole, voriconazole, and caspofungin. The isolate of T. asahii was only sensitive to nystatin and amphotericin B. According to the laboratory and clinical results, nystatin is recommended for most patients. Finally, it is better to prescribe the antifungal drugs in each center according to their reported sensitivity.