Sensorineural hearing loss (SNHL) is known to be associated with lesions at various sites, including outer hair cell (OHC) and inner hair cell (IHC) injury, as well as auditory dyssynchrony or vestibulocochlear nerve tumors. Therefore, it is important to establish the differential diagnosis of SNHL, which however is particularly challenging in patients with unilateral SNHL. The test battery approach is effective for accurate diagnosis in such cases. In this report, we discuss the usefulness of the test battery approach to accurately detect the site of the lesion in a patient with unilateral hearing loss. A 14-year-9-month-old adolescent who observed decreased hearing sensitivity in the left ear accompanied by difficulty with understanding speech at a distance was diagnosed with unilateral hearing loss in the left ear. In this report, we describe a rare and diagnostically challenging case of unilateral SNHL in a patient with normal OHC function and selective injury to IHCs, which was diagnosed using a test battery approach.