Recently, IFN-free NS5A inhibitor daclatasvir and protease inhibitor asunaprevir combination treatment was approved for genotype 1b HCV-infected patients who were ineligible or who failed to respond to previous therapies. NS5A inhibitor-resistant variants occasionally exist in HCV-infected patients who have never been exposed to direct-acting antivirals. In Japanese HCV genotype 1b-infected patients, the frequency of NS5A inhibitor-resistant variants is approximately 11-23 %. The phase 3 study of daclatasvir and asunaprevir combination therapy showed that more patients with NS5A 31 and/or 93 resistance-associated variants experienced virological failure. Preexisting NS5A inhibitor-resistant variants should be evaluated carefully before choosing the drugs.