Flavonoids present a group of polyphenolic compounds present in almost all higher plants. They make one of the largest groups of secondary plant metabolites and are easily recognizable as pigments responsible for the color of leaves and flovers. They have numerous significant roles in plants and a positive effect on humane health. A spectroscopic characterization of galangin, kaempferol and myricetin, three flavonoids structurally related to quercetin, which is the widest spread flavonid in plants, was carried out in this study. Interactions of these flavonoids with lanthanum(III) as well as interactions of La(III)- flavonoid complexes with different DNA and RNA polynucleotides were also investigated by UV/Vis titrations. The results confirm a significant affinity of La(III)-galangin and La(III)-kaempferol toward investigated double stranded (ct-DNA, poly A - poly U, poly G - poly C) and single stranded (poly A, poly U, poly G, poly C) polynucleotides. The interactions of La(III)- miricetin with those polynucleotides did not give expected results because during the experiments precipitation occurred. La(III) is of considerable importance for the stability of the flavonoid-La(III)-polynucleotid complex as well as for significant changes in the UV/Vis spectra. Comparison of here presented results with the previous studies of galangin, kaempferol and miricetin with same polynucleotides but without La(III), pointed that the presence of La(III) has significant influence in binding La(III)-flavonoid complex on polynucleotides.