A tuning key for guitar strings is provided, which enables the remaining portion of guitar strings which is left after being wound on the tuning key when the guitar strings are hung and set. The tuning key for guitar strings comprises a tuning peg on which a worm gear portion is arranged at one side, a coupling body in which a male screw portion is formed, a casing in which a bearing portion is formed, a rotary rod in which a spur gear is arranged, and a nut coupled to the male screw portion of the casing and fixes the casing from a head, wherein tuning keys for guitar strings are provided in the head, and a through-hole through which the remaining portion of guitar strings wound on a winding portion is penetrated and arranged is formed in the center of the rotary rod.