Different methods can be used to treat the malignant disease; surgery, radiotherapy, chemotherapy, and even cryotherapy are different approach to reach the best treatment for patients. The aim of this cross sectional study was to evaluate the prevalence of oral side effects followed by chemotherapy of cancerous patients in Imam Khomeini hospital. This study was conducted on 80 patients who were under chemotherapy more than once and their oral lesions were evaluated considering their physical conditions. Mucositis was the common problem (66.2%) and the most involvement area was observed in tongue (55%). High percentage of this lesion in adult and senile might be due to deficiency in their immune system.