A lotof algae fossilswere found in Cenozoic lake sediments especiallyPediastrum fossil sed-imentar'y deposits in some places of China and also in some nearby seacoasts. For imitating Pedi-astrum mine ralization in lake sediments several species ofPediastrum are cultured using BBM medium and sea water with 18% salt. By optical and electronic microscope observation and photo-syntheic pigment analysis we found thatPediastrum boryanum,P. duplex var'clathratum andP.tetras etc. cannot grow well in sea water. If cultured in saline medium the specimen will die in a short period of time. We consider that probably thePediastrum fossil that appeared in marine sediments were transported to the sea by river. In order to prove the mineralization condition of in living organism and fossils ofPediastrum, the following analy sis is made. The fat-soluble substances are high and they contain a small amountof alkane alkene fatty acid and a great deal of plant pigments.Pediastrum has high H/C and low 0/C (atom number ratio) value. Therefore,it is agood resource of oilformation. The products of oxidative degradation of the insoluble cell-wall ofPediastrum are similar to the production obtained by kerogen, which is known to be of algalorigin. So the insolable materials of cell-wall are probably a source of kerogen during the deposition.