Objective The aim is to investigate the effect of ambroxol on radiation lung injury and the expression of transforming growth factor β1(TGF-β1),and tumor necrosis factor α(TNF-α)in plasma. Methods Ninety-eight patients with locally advanced lung cancer in radiotherapy were randomized into treatment and control groups.Patients in the treatment group took ambroxol orally at a dosage of 60 mg,three times per day for 3 months from the beginning of radiotherapy.The expression of TGF-β1 and TNF-αin plasma was analyzed.The clinical symptoms and lung diffusing capacity were monitored using high resolving power computed tomography. Results The level of TGF-β1 in the control group was increased(11.8 ± 5.5 ng/mL),whereas in ambroxol-treated patients,the increase was not significant(5.5 ± 2.6 ng/mL,P＜0.001). Radiotherapy-induced elevation of TNF-α levels,seen in control patients,was also abolished after treatment with ambroxol(5.1 ± 1.3 vs 2.6 ± 0.8 ng/mL,P＜0.001). Conclusion Ambroxol can obviously decrease the plasma TGF-β1 and TNF-α levels after radiotherapy,and decrease the chances of early radiation pneumonitis and late pulmonary fibrosis,and improve treatment effect and quality of life of patients.