Objective To explore the reasonable clinical target volumes by analyzing the characteristic of mediastinal lymph node metastases in non-small-cell lung cacer (NSCLC).Methods 291 NSCLC patients was performed pre-therapy CT scans,and the incidence of mediastinal lymph node metastases was analysed.Results Among the 152 patients with right lung NSCLC,the incidence of involvement of the ipsilateral supraclavicular lymph nodes was 15.8 ％ (24/152),and the incidence of involvement of the contralateral lymph nodes was 6.6 ％ (10/152).The highest incidence of mediastinal nodal involvement occurred in the ipsilateral hilar nodes (59.2 ％),followed by area 4R (56.6 ％),area 1-2R (36.2 ％),area 7 (33.6 ％),area 4L(20.4 ％),area 10-11L (5.9 ％),area 6 (3.9 ％),area 5 (2.0 ％),area 1-2L (2.0 ％),respectively.Among the 139 patients left lung NSCLC,the incidence of involvement of the ipsilateral supraclavicular lymph nodes was 15.8 ％ (23/139),and the incidence of involvement of the contralateral lymph nodes was 5.8 ％ (8/139).The highest incidence of mediastinal nodal involvement occurred also in the ipsilateral hilar nodes (54.0 ％),followed by area 7 (33.8 ％),area 4R (26.6 ％),area 4L (24.5 ％),area 1-2R (15.8 ％),area 5 (10.8 ％),area 6 (9.4 ％),area 1-2L (5.8 ％),area 10-11R (5.0 ％) respectively.Conclusion The right side primaries or left side primaries of NSCLC have different high risk lymph node areas for metastasis,and selective irradiation to these lymph node areas maybe increase the tumor control rate and reduce the recurrence rate.