During the course of study on the biological active compound from Ligia exotica, various nucleic acids such as guanosine, deoxyguanosine, inosine, deoxyinosine, and 3``-O-glucosyl-inosine have been isolated as a new inosine nucleic acid derivative. The new nucleic acid was purified from fraction 8 of Sephadex G10 chromatogram(L. exotica) by high press liquid chromatography on GS 320 and ODS column. In order to determine the structure of the compound, which was isolated from L. exotica, its $^1H$ NMR and $^{13}C$ NMR were compared with those from 5``-O-glucosyl-inosine and 3``-O-galactosyl-inosine. Chemical synthesis and enzymatic formation of 3``-O-galactosyl-inosine is being studied.