Chen chose the path of research after completing his residency. His mentor was Professor Sung Jui-lou, then NTU's authority on liver disease, and thus began Chen's development in the field of liver disease research.
受完住院醫師訓練後，陳定信選擇走研究之路，師承當時台大肝病權威──宋瑞樓教授，從此一頭栽入肝病研究的領域中。