Abstract: Objective Evaluate the early response and toxicity of concurrent chemoradiotherapy.Methods Eighty unresectable stage III_a-III_b NSCLC patients pathologically proved were randomly divided into 2 groups.Group A:patients were treated with concurrent chemotherapy of paclitaxel(100mg/m², on day2.)and cisplatin(30mg/m², on days 2-6)(TP regimen)plus 3-dimensional conformal radiotherapy.The total dose was 60Gy-70Gy.After the radiation, 3 cycles of TP regimen were performed, but the dose of paclitaxel was 200mg/m².Group B:patients received sequential chemoradiotherapy.First radiation was performed as same as group A.Then chemotherapy of TP(paclitaxel 200mg/m², on day 2, DDP 30mg/m², on days 2-6)was followed for 4-5 cycles.Results The overall response rate in concurrent and sequential groups was 80.0%and 57.5% respectively(χ² =4.71, P＜0.05).Incidences of grade III-Ⅳ acute radiation esophagitis, leukopenia, nausea/vomiting and skin reaction were 47.5%, 42.5%, 52.5% and 57.5% in group A, and 25.0%, 17.5%, 30.0% and 17.5%in group B respectively(P＜0.05).Incidences of grade III-Ⅳ acute radiation pneumonitis and lose hair rate was 32.5%, 7.5% in group A and 20.0%, 27.5%in group B respectively(P＞0.1).Conclusion Concurrent chemoradiotherapy is well tolerated in most unresectable stage III_a-III_b NSCLC patients.Its early response is better than sequential chemoradiotherapy.