The affinities of apigenin, chrysin, daidzein and quercetin for human serum albumin (HSA) were studied in the presence and absence of Pb2+, Ni2+, Zn2+, Mg2+ and Mn2+. The fluorescence intensities of HSA decrease remarkably with increasing concentration of these four flavonoids. Adding apigenin and chrysin resulted in blue-shifts of HSA from λ em=336 to 332 nm and 330 nm, respectively. However, quercetin showed an obvious red-shift of HSA from λ em=336 to 347 nm whereas daidzein hardly affected the λ em of HSA. The λ em shifts induced by flavonoids in the presence of mental ions were much bigger than those in the absence of these ions. Pb2+, Ni2+, Zn2+, Mg2+ and Mn2+ increased the quenching constants of these four flavonoids for HSA by 19.2 % to 43 %, 47.7 % to 117 %, 23.3 % to 64.4 %, 9.29 % to 42.2 % and 18 % to 55.6 %, respectively. The affinities of apigenin, chrysin, daidzein and quercetin for HSA increased about 9.49 %, 3.63 %, 5.73 % and 2.32 %, respectively, in the presence of Pb2+. Ni2+ improved the affinities of apigenin, chrysin, daidzein and quercetin for HSA by about 4.79 %, 0.85 %, 11.91 % and 10.55 %, respectively. Zn2+ enhanced the affinities of apigenin, chrysin, daidzein and quercetin for HSA by about 1.03 %, 1.34 %, 1.96 % and 13.14 %, respectively. Mg2+ increased the affinities of apigenin, chrysin, daidzein and quercetin for HSA by about 2.03 %, 0.7 %, 1.39 % and 2.07 %, respectively. Mn2+ increased the affinities of apigenin, chrysin, daidzein and quercetin for HSA by about 2.46 %, 6.71 %, 12.3 % and 4.10 %, respectively.