In order to study the biological effects of the flavans on coleoptile growth of oats (Avena sativa L.), the total flavan contents (Catechin, epicatechin, biflavan and oligomer flavan), one of phenolic compounds in phloem tissues of annual shoots of walnut collected monthly for one year were detected by TLC (Thin Layer Chromatography). Coleptile developments in the mediums of Flavan, Flavan+ IAA, IAA (Indole acetic acid), and control treatments were evaluated. Flavans inhibited the coleopthyl growth between 6.30 % and 12.73 % in all months according to control treatments. On the other hand, chip-buddings were made each month, and the total flavans in phloem tissues were also determined. Therefore, the graft success and changing of the total flavans in the annual shoots according to months were discussed compared with the inhibiting effects of the flavan treatments. Both the inhibiting percentages of the flavans on coleopthyl growth and also the total flavan contents in the annual shoots were found to be higher in May, July and August months when the graft success was lower. Namely, the total flavans in the plant structure and their biological effects in the flavan medium showed a negative relation with the graft success in these months. But, similar relations were not recorded in all months. The results revealed that graft success might not depend on only the flavan contents in the structure, but also other factors such as anatomical structure, hormonal conditions of the rootstock and scion, and graft technique, etc.