This invention relates to a process for preparing high-purity aromatic oligomers by effectively separating an organic layer containing aromatic oligomers or the reaction products of a polycyclic aromatic compound with formaldehyde from an aqueous layer containing an acid catalyst in a simplified manner, hitherto regarded difficult to accomplish, and obtaining high-purity aromatic oligomers from the organic layer containing a reduced amount of impurities. In separating the aqueous layer containing the acid catalyst and the organic layer containing the oligomers from the reaction mixture formed by the condensation of a polycyclic aromatic compound and formaldehyde, the emulsion phase is broken by adding a nonionic or cationic surfactant in an effective amount and an alkali in an amount sufficient to neutralize 1-70% of the acid in the acid catalyst, the organic and aqueous layers are separated and the aromatic oligomers are recovered from the organic layer.