Alectinib, a novel alternative anaplastic lymphoma kinase (ALK) inhibitor, is highly effective against ALK-positive non-small cell lung cancer (NSCLC) and is well tolerated. Molecular targeted agents generally have little contribution to alopecia. We encountered a case of alopecia that developed gradually over 2 months after initiation of alectinib administration for the treatment of ALK-positive NSCLC. The patient had no history of alopecia in previous treatments of cisplatin + pemetrexed and crizotinib. The present case indicates that alopecia should be taken into consideration as toxicity during alectinib treatment, which could adversely affect the psychological and emotional condition and quality of life even in patients treated with specific molecular targeted agents.