Abstract: bjective To investigate the incidence of radiation pneumonitis（RP）in patients with lung cancer and esophageal cancer irradiated with helical tomotherapy（HT） and the occurrence of RP with dose volume histogram（DVH）and clinicopathologic features. Methods Nineteen lung cancer and 14 esophageal cancer patients treated by HT were analyzed retrospectively. Thirteen of the 33 patients received HT alone and 20 patients were treated in combination with chemotherapy. Radiotherapy was delivered to total dose of 54-61.8Gy／27-28f，54-66Gy／25-31f and 60-66Gy／28-30f for small cell lung cancer，non-small cell lung cancer and esophageal cancer. Results RP grade of 0, 1, 2, 3 and 5 occurred in 8（24.2％），15（45.4％），1（3.0％），5（15.2％） and 4（12.1％）cases in all the patients，respectively. DVH parameters analysis showed that≥grade 2 RP was associated with V30-V45，but not with V5-V25，mean lung dose（MLD）and planning target volume（PTV）. Meanwhile，≥grade 2 RP was related to ECOG score，but not with lung cancer/esophageal cancer, gender, age，smoking，chemotherapy and chronic obstructive pulmonary diseases. Conclusion The incidence of RP is not high in patients with lung cancer and esophageal cancer treated by HT. Patients with poor ECOG score and late stage should have even strict limitation of DVH.