Abstract: Tetraselmis,a unicellular green algae located uniquely in phytophylogeny,is a new important model organism for the study of the origin and evolution of green plants.The genomic DNAs of Tetraselmis are difficult to be isolated because of its hard theca and unique cell wall components,as well as its richness in glycoprotein easy to impurify the genomic DNA.We reported here that an improved low pH extraction matrix with high salts originally developed for higher plant was successfully to obtain high quality of genomic DNA of Tetraselmis.Compared to the traditional CTAB extraction,this approach is very fast and economical just by changing extraction medium so that the efficiency of Tetraselmis cell breakage was greatly improved,and the pollution of proteins released during DNA extraction were drastically reduced as well.The fragments of Tetraselmis nuclear ribosome internal transcribed DNA spacers (nrDNA ITS) were PCR amplified successfully from this minipreparations of the genomic DNA,but also amenable to nrDNA ITS sequencing.Due to its application to some higher plants whose genomic DNAs are hard to be iso lated,this improved method of low pH extraction matrix with high salts we described here for the marine unicellular microalga Tetraselmis could be right for the minipreparation of genomic DNA of other unicellular or multicellular fresh and marine algae.