A process for purifying a phenol derivative selected from alkylphenols having a number average molecular weight of from 200 to 4 000 and Mannich adducts thereof is described, in which the phenol derivative is brought into intimate contact with an extracting agent having a polarity E.sub.T(30) of from 57 to 38 kcal/mol, a phase containing the phenol derivative and an extracting agent phase are allowed to separate from one another and the extracting agent phase is removed.