Abstract: Objective 　To evaluate ret rospectively the correlative clinical and dosimetric factors resulted in acute esophageal toxicity in the course of the t reatment of the patient s with stage Ⅲ non-small cell lung cancer with three-dimensional conformal radiotherapy. Methods 　Seventy six patients with NSCLC were treated with 3D-CRT between august 2002 and december 2005. The clinic factors and treatment parameters were collected and coded. Acute esophageal toxicities were graded. All factors correlating with acute esophageal toxicity were analyzed. Results 　27 patients (35. 53 %) out of the seventy-six patient s had developed acute esophageal toxicity according to RTOG scores. The acute esophageal toxicities were graded : I-15 、II-6 、Ⅲ-6. Spearman rank correlation coefficients had showed that chemotherapy, percentages of esophagus volume receiving > 50 Gy(V50 ), the average dose to the esophagus, correlated with acute esophageal toxicity. Binary logistic regression analysis showed chemotherapy, esophageal V50, were the independent risk factors of acute esophageal toxicity. Conclusion 　Concurrent chemotherapy and the maximal esophageal point dose ≥50 Gy significantly related to the acute esophageal toxicity in patients with stage III NSCLC treated with 3D-CRT.