Penetration-aspiration is the most serious complication in patients with nasopharyngeal carcinoma (NPC) after radiotherapy. Radiotherapy has been shown to increase the patient's survival rate and life expectancy but it showed serious side effects such as oropharyngeal dysphagia. It’s related morbidity and mortality such as penetration-aspiration could progress to aspiration pneumonia, sepsis, and death if not treated properly. Factors suspected to be the determinants of penetration-aspiration were the location of the pharyngeal residue, the stage of NPC, and the time after radiotherapy. This primary objective of this study was to determine the clinical factors of penetration-aspiration in patients with NPC after radiotherapy. In a cross sectional, observational analytic study, a total of 24 patients were obtained with consecutive sampling technique. Fiberoptic endoscopic evaluation of swallowing (FEES) examination was performed on patients with NPC after radiotherapy to assess pharyngeal residue and penetration-aspiration. The Yale Pharyngeal Residue Severity Rating Scale (YPR-SRS) and the Penetration-Aspiration Scale (PAS) was used to assess the presence of pharyngeal residue and penetration-aspiration, respectively. Statistical analysis used multiple logistic regression (p