This study investigated the feasibility of using ultrasound to distinguish the post-radiotherapy (post-RT) changes of parotid glands in nasopharyngeal carcinoma (NPC) patients treated with intensity modulated radiotherapy (IMRT) or conventional radiotherapy. A total of 60 NPC patients (30 received IMRT and 30 received conventional RT in 2000-2006) with different degrees of xerostomia were recruited. Grey-scale ultrasound examination of parotid glands was performed on each patient. The parotid glands were assessed for their size, echogenicity, echogeneity, echotexture and conspicuity of intra-glandular ducts. Each patient was also asked to complete a xerostomia questionnaire. Result showed that the parotid glands of patients treated with conventional RT were smaller than those in patients with IMRT. Parotid glands of patients with conventional RT were generally heterogenous, isoechoic to adjacent muscle, with more hypoechoic focal areas and the intra-glandular ducts more obviously seen on ultrasound. However, parotid glands of patients with IMRT were more homogenous, hyperechoic to adjacent muscle, with less or absence of hypoechoic focal areas and the intra-glandular ducts were marginally seen. To conclude, ultrasound is useful in the assessment of post-RT changes of parotid gland, and has potential to be used for distinguishing the level of radiation induced changes of salivary glands.