e20611 Background: Concurrent chemoradiotherapy (CCRT) is the main treatment for patients of unresectable stage Ⅲ non-small cell lung cancer (NSCLC).To retrospectively analyze prognosis and its related factors for patients of unresectable stage III NSCLC after radiotherapy in different periods. Methods: From 2000 to 2010 and from 2015 to 2019, patients of stage III NSCLC which received radiotherapy in the Fourth Hospital of Hebei Medical University were enrolled. Statistical analysis was used with the SPSS 21.0 software.The Kaplan-Meier method, log-rank test and Cox model were used for survival analysis, univariate analysis, and multivariate analysis, respectively. Results: A total of 808 patients of stage III NSCLC were enrolled. There were 674 males and 134 females. The median age was 63 years old( 29-86 years old ) . Radiotherapy (RT) were performed in 474 patients between 2000 to 2010 and in 334 patients between 2015 to 2019. There were 240 cases received with RT alone, 449 cases with sequential chemoradiotherapy (Seq-CRT) and 119 cases with CCRT. 55 were treated with 3-dimensional radiotherapy (2DRT) plus 3-dimensional conformal radiotherapy (3DCRT),386 with 3DCRT,and 367 with intensity-modulated radiotherapy(IMRT), respectively. The median doses was 60 Gy (range 36-77Gy). The median overall survival (OS) was 21.0 months (19.4-22.6 months), and the 1-, 3- and 5-year OS rates were 69.8%, 30.7% and 21.3%, respectively. Under univariate analysis, gender, age, radiotherapy technology,period of treatment and whether combined chemotherapy were significantly associated with OS ( P< 0.05). The median OS was 18.0 months in group of 2000-2010 and 26.1 months in group of 2015-2019, respectively. The median OS for groups of2DRT+3DCRT, 3DCRT and IMRT were 10.0, 21.0, 23.4 months, respectively. The median OS for RT alone, Seq-CRT and CCRT was 17.0, 21.0, 30.3 months, respectively. Under multivariate analysis, sex, age, times of RT and combined chemotherapy were independent prognostic factors for OS ( P< 0.05). Conclusions: From 2DRT to 3DCRT or IMRT, the OS in patients of stage Ⅲ NSCLC was gradually increased; the OS was more higher in patients treated between 2015-2019 also. In addition, the OS was significantly longer in patients with CCRT than with Seq-CRT or RT alone.