Afatinib, a second-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, is efficacious as first-line treatment in patients with EGFR-mutated non-small cell lung cancer (NSCLC). Dosage reduction is recommended in patients with intolerable adverse events; however, data regarding the efficacy of low-dose afatinib are limited. We report the case of a 71-year-old female patient who was diagnosed with advanced EGFR-mutated NSCLC and started treatment with oral afatinib 40 mg daily. The patient achieved partial tumor response on computed tomography imaging, but developed unacceptable skin-related toxicities requiring dosage reduction to 20 mg daily. The patient subsequently achieved complete tumor response and showed improvements in performance status. These observations suggest that low-dose afatinib is effective in patients with EGFR-mutated NSCLC who require dosage reduction for intolerable adverse events.