This study found that in Tris-HCl buffer, the resonance light scattering (RLS) intensity of the Eu(3+)-nicotinic acid system can be greatly enhanced by nucleic acids and the enhanced intensity is proportional to the concentration of nucleic acid in the range of 7 x 10(-8)-1 x 10(-5 ) g x mL(-1) for fsDNA, and its detection limit is 2 x 10(-8 ) g x mL(-1). Based on this, a new method for the determination of nucleic acids is proposed. Synthetic and actual samples are determined satisfactorily. The interaction mechanism is also studied. It is thought that nucleic acid can bind with the Eu(3+)-nicotinic acid complex through electrostatic attraction and thus form a large Eu(3+)-nicotinic acid-nucleic acid complex.