Afatinib is an epidermal growth factor receptor-tyrosine kinase inhibitor(EGFR-TKI). In a randomized phase III study(Lux- Lung 3 study)employing patients harboring EGFR mutations, patients administered afatinib show a significantly longer progression free survival time(PFS)than those administeredcombination chemotherapy comprising cisplatin andpemetrexed . However, most of the patients(95.2%)treatedwith afatinib experiencedd iarrhea. In the present report, 16 patients with EGFR mutations were treatedby afatinib at our institution from May 2014 to December 2014. Twelve patients were administered a diarrhea prevention herbal medicine, Hange-shashin-to. Seven of 12 patients(58%)had no diarrhea during the 28 days of therapy. All 4 of the patients who did not receive Hange-shashin-to experienced diarrhea above Grade 1 within 6 days of starting therapy. The rate of diarrhea differed significantly between the patients receiving and not receiving Hangeshashin- to. In conclusion, preventive administration of Hange-shashin-to may reduce the occurrence of diarrhea during afatinib treatment.