Abstract: The 18S rRNA genes were sequenced from green algae Ulva pertusa, Enteromorpha prolifera and Monostroma latissimum and compared with other algae E. intestinalis , U. fenesrtata , U. lactuca , M. nitidum , and M. grevillei to evaluate the basic composition and sequence divergence among their sequences in the phylogenetic tree. There was more Kimura 2 - parameter distance between E. prolifera and E. intestinalis than those among E. prolifera and three Ulva species. The phylogenetic trees in UPGMA and MP manners were almost identical. The phylogenetic tree supported E. prolifera gathered together with Ulva pertusa. There was more close genetic relationship between E. prolifera and Ulva species than those between E. prolifera and E. intestinalis.