To produce the above high-purity phenol in high selectivity under mild reactional conditions by passing a specific alkyl-substituted phenol through a step for reaction with an aldehyde and a carboxylic acid, etc.

(A) A tert-alkyl-substituted phenol having formula II [R1 and R2 are each a 1-12C alkyl, a 5-8C cycloalkyl, phenyl, etc.; (m) is 0, 1 or 2] in which at least one of the o- and p-positions with respect to OH group is unoccupied is reacted with (B) 1-20mol formaldehyde or its polymer and (C) 1mol carboxylic acid of the formula R3-COON (R3 is H, a 1-18C alkyl, etc.) to produce a mixture of compounds of formula III [(o) is 1-8; (n) is 1 or 2] with formula IV, [(p), (q) and (r) are each independently 1-8] which is then hydrogenated with H2 in the presence of a hydrogenating catalyst to provide a substituted phenol of formula V when obtaining the objective phenol of formula I having the methylated or dimethylated o- or p-position with respect to the OH group. When (m) is 0, the tert-alkyl group is cleaved in the presence of an acid cleaving catalyst at 80-300°C.