A process for production of phenolic novolak which comprises the step of conducting heterogeneous reaction of a phenol with 0.40 to 0.93 mol of an aldehyde per mol of the phenol in the presence of at least 25 parts by mass of a phosphoric acid per 100 parts by mass of the phenol. This process can give in high yield phenolic novolak with the contents of monomeric and dimeric phenols and a degree of dispersion controlled.