To investigate the influence of prophylactic elective nodal irradiation on the therapeutic results of definitive radiotherapy for patients with stage IIIA or stage IIIB unresectable non-small-cell lung cancer, 55 patients with clinically inoperable advanced non-small-cell lung cancer were studied. After four cycles of induction chemotherapy, the patients were divided into two groups at random. In one group, the elective nodal irradiation was included in clinical tumor volume (CTV) of definitive radiotherapy (ENI group); and in the other group, elective nodal irradiation was not included in CTV (non-ENI group). For the patients in the ENI group, the mean prescription dose for gross tumor volumes was 58.4 Gy, while for the patients in the non-ENI group, it was 65.8 Gy (<0.05). The responsive rates were 45.8% and 74.0% (<0.05), and the rate of the elective nodal failure (ENF) was 4.2% and 11.1%, respectively. Kaplan-Meier analysis showed that the mean local-progression-free survival time was 11.0 and 15.0 months, and one-year local-failure rates were 51.9% and 24.5% (<0.05). The median overall survival time was 13.0 and 15.0 months, respectively ( = 0.084). The one-year survival rates were 55.7% and 72.5%, and two-year survival rates were 0% and 19.9%. There was no significant difference in the occurrences of radiation-associated complications between the two groups. Our results showed that omitting elective nodal irradiation did not result in a high incidence of elective nodal failure. On the contrary, it decreased local failure by increasing prescription doses to the primary diseases and lymphadenopaphy, and thereby it may further prolong the patients survival.