A process for producing a 3,3,5-trimethylcyclohexylidenebisphenol, comprising pre-reacting a phenol (A), i.e., phenol whose 2- and 6-positions may be monosubstituted or disubstituted with an alkyl group having 1 to 4 carbon atoms, with 3,3,5-trimethylcyclohexanone (B) at a molar ratio ((A)/(B)) of 3 to 7 in the presence of an acid catalyst until 3,3,5-trimethylcyclohexanone (B) exhibits a degree of conversion of at least 90 mol %; adding the phenol (A) and/or an aromatic hydrocarbon (C) to the thus obtained reaction mixture; and post-reacting the resultant mixture. This process enables not only suppressing a rise of the viscosity of the reaction mixture but also obtaining the desired product at high yield. Therefore, this process is applicable to not only the productivity enhancement in batch processing but also a continuous reaction processing which has been regarded as being difficult.