The effects of some phenolic compounds on the growth of Piricularia oryzae and Cochliobolus miyabeanus and on brown coloration of the media during culture were studied by the addition of each of these compounds of the final concentration of 10^-3 or 10^-4 M to the synthetic medium (Tomizawa's medium) before the culture. Results obtained from the experiments carried out at 27℃. were as follows : 1. Rutin and phloroglucinol of 10^-3M each, promoted significantly the mycelial growth of C. miyabeanus ; protocatechuic acid also showed the same tendency at the same concentration. Whereas caffeic acid, gallic acid and catechol showed no remarkable effect (Fig. 1) for the first 10 days. 2. The medium added with rutin, protocatechuic acid, caffeic acid and catechol at the concentration of 10^-3M respectively turned brown during the early stage-up to 5 days of the culture of C. miyabeanus ; then, discoloration occurred gradually at about 15 days from the beginning in case of rutin and at about 5 days in case of the other o-dihydroxyl type phenols (Fig. 2). 3. Phenolic compounds added to the synthetic media were degra d ed gradually along with the growth of C. miyabeanus (Fig. 3). 4. In the synthetic medium containing catechol ( 10^-3M) C. miiyabeanus utilized each of sugars, added as the carbon sources, in the following descending order : sucrose, maltose, glucose, xylose, fructose, arabinose and rhamnose (Fig. 4). While the degrees of browning of the same culture solutions containing each of these sugars differed with each other in the following descending order when measured after 7 days from inoculation : maltose, sucrose, fructose, xylose, glucose, arabinose and rhamnose. However, the order of the degree of browning of the media was changed markedly with the progress of culture (Fig. 5). 5. The mycelial growth of P. oryzae was inhibited almost completel y by the presence of 10-3M of each of catechol, caffeic acid, and gallic acid, though it was affected scarcely by the same concentration of each of phloroglucinol, protocatcchuic acid and rutin. The growth of P. oryzae was somewhat inhibited by the presence of 10-4M of gallic acid, caffeic acid and catechol, whereas it was not affected by the other phenolic compounds used at the same concentration (Fig. 6). 6. P. oryzae turned the media brown (the media to which each of rutin, protocatechuic acid, catechol or caffeic acid of 10^-4M respectively was added). The media which had once become brown were somewhat discolored during 5 to 10 days after inoculation (Fig. 7). 7. It was suggested that the discoloration occurred in later stage of the culture was the result of the decomposition of once oxidized phenols or newly produced pigments by the fungi.