The present invention provides efinaconazole producing and purifying methods adapted to industrial scale that provide high-purity efinaconazole in high yield by simple operations using specific impurities as indices. The efinaconazole producing method comprises:step A of forming a toluene solution comprising compound (II), compound (III), an inorganic base, and toluene in a volume (L) which is 2 to 5 times the mass (kg) of compound (II)；step B of subjecting the toluene solution to reaction under heating；step C of washing the reaction mixture from step B to obtain a toluene solution of crude efinaconazole in which the residual amount of 4-MP is not more than 5 wt % of efinaconazole.
