The relationships between molecular structures of dietary flavonoids and their affinities for bovine serum albumin（BSA） were investigated by fluorescence titration analysis.The results indicated that the binding process with BSA was significantly affected by the molecular structures of flavonoids.The methylation of hydroxyl groups in flavonoids could enhance their binding affinities for BSA by 1 to 794 times.Hydroxylation on rings of A,B and C also strongly influenced the affinities for BSA.The glycosylation weakened the affinities for BSA by 1-2 orders of magnitude depending on the conjugation site and the class of sugar moiety.The hydrogenation of the C2‖C3 double bond slightly decreased the binding affinities.The galloylated catechins and pyrogallol type catechins exhibited higher binding affinities for BSA than the non-galloylated catechins and catechol-type catechins,respectively.The affinities for BSA increased with the increase of partition coefficients and decreased with the increase of hydrogen bond donor and acceptor numbers of flavonoids,which suggested that the binding interaction was mainly caused by hydrophobic forces.