A fixing structure of a faucet fixed on a support plate with an opening and contains the faucet including a housing having a mouth and a through aperture; the faucet also including an inlet pipe unit; a locking member being operated to move between an engaging position and a disengaging position along the through aperture; a positioning device including a fitting seat having a bottom face, a channel defined therein to receive the inlet pipe unit of the faucet, at least one slot disposed along an outer surface thereof to slide the locking member located at the engaging position, the slot including at least one tooth and at least one retaining recess such that the locking member passes through the tooth to be retained in the retaining recess and is limited by the tooth to move so that the mouth is fixed to the fitting seat.