Background: This study is conducted mainly to evaluate the changes in quality and quantity of oral epithelial cells during the course of IMRT. Material and Methods: 30 Patients undergoing chemo-radiotherapy were followed through course of treatment. They were compared with a group of age- and sex-matched healthy individuals. The procedure involved WHO clinical scoring, collection of oral washings and preparation of buccal smears from both study group and control group. The changes occurred were recorded as a way of assessing the severity of oral mucositis. Results: revealed a significant occurrence of oral mucositis in almost all patients during weekly follow up. There was a significant increase in percentage of viable buccal epithelial cells in study group when compared to normal controls ( P <0.005) during and at the end of chemo-radiotherapy. Conclusion s : quantification of oral mucositis can be done at cellular level by determining the oral mucosal cell viability and their maturation during IMRT.