Lasers and photodynamic therapy have been considered a convergence treatment for onychomycosis, which is a fungal infection on the nail bed and nail plate. Laser therapies have shown satisfactory results without significant complications for onychomycosis; however, the mechanism of clearing remains unknown. In this work, we investigated changes in the chemical structure of nail keratin induced by Nd: YAG laser using Raman spectroscopy. Toe nails with onychomycosis were treated with 1064 nm Nd: YAG laser. After laser treatment, the disulfide band (490-590 cm(-1)) of nail keratin was rarely observed or was reduced in intensity. The amide I band (1500-1700 cm(-1)) also showed changes induced by the laser. The a-helical (1652 cm(-1)) structures dominated the beta-sheet (1673 cm(-1)) in nontreated nail, but the opposite phenomenon was observed after laser treatment.