A method for hydroxylating phenols and phenol ethers using hydrogen peroxide and specifically, a method for hydroxylating phenol using hydrogen peroxide. The method for hydroxylating a phenolic substrate selected from a phenol or a phenol ether by reacting such phenolic substrate with hydrogen peroxide in the presence of an acid catalyst comprises the following steps, implemented consecutively or simultaneously: a first step consisting of mixing a phenolic substrate with a hydrogen peroxide solution under conditions in which the temperature is sufficient for the initial phenolic substrate to remain liquid and for minimizing the conversion rate of the hydrogen peroxide; a second step consisting of carrying out the phenolic substrate hydroxylation reaction under adiabatic conditions, the acid catalyst being added at the mixing stage and/or at the beginning of the hydroxylation reaction; and a third step, if necessary, consisting of recovering the hydroxylated product.