Abstract: The field desorption mass spectra of nucleosides are simple, only showedintense M~+, M+1~+, M+K~+ and the characteristic sugar S, base B+H cleavage fragments. The field desorption mass spectra of nucleic acids arecomplex compared with the field desorption mass spectra of nucleosides, exceptfor showing structural information, but fragment ions of phosphoric acids andphosphates have been observed. The field desorption mass spectra of nucleosi-des and nucleic acids supplied important information for determining their stru-cture.