Sensorineural olfactory dysfunction is caused by damage in the olfactory neuroepithelium and central olfactory pathway. Although many types of drugs, such as zinc preparations, Chinese medicine, topical and systemic steroids, vitamins, and metabolic agents have been tested for the treatment of sensorineural olfactory dysfunction, none of them have been shown to be effective in placebo-controlled randomized controlled trials. In 2009, Hummel et al. reported that olfactory training using odorants was effective in improving sensorineural olfactory dysfunction. In their study, the patient group which did olfactory training with four odorants (phenylethyl alcohol (rose), eucalyptol (eucalyptus), citronellal (lemon), eugenol (clove) twice a day for 12 weeks showed better improvement of the olfactory function after the intervention period than the patient group which did not do the training. Since then, various protocols to change the intervention period, number of odorants, and intensity of odors have been tested for improving the efficacy. The cellular mechanism of why olfactory training is effective for the treatment of sensorineural olfactory dysfunction in humans is unknown, but based on the results of animal studies, it may reflect the olfactory input-dependent survival of olfactory receptor neurons in the neuroepithelium and granule cells in the olfactory bulb. A multi-center study of medical institutions in Japan is currently underway to establish a Japanese-style olfactory training program.