Abstract: Studies on the mass culture of Scenedesmus obliquus and Chlorella pyrenoidosa have been going on since July 1958.The algae were isolated from Dung-hu Lake,Wuchang(Hupeh),and first cultivated in the laboratory under artificial illumination.Then,following Michurin's principles, the cultivation of the stock was continued in the open,to induce adaptations to the environmental factors which will be encountered in outdoor mass culture. The vessels used for the cultivation of Scenedesmus obliquus were 4 shallow round wooden trays,1.5 metres in diameter,and they were kept on the laboratory roof.The algae were grown in HB No.4 and HB No.6 culture media,replenished every 3 days.About 4—7 days after inocula- tion,the dry weight of the algae increased from 50 mg.per litre to 400—500 mg.per litre.When the algae were cultivated in HB No.6 medium,the concentration potential increased more quickly than that in HB No.4,but the colour became yellowish green,and the logarithmic phase was maintained for only 4 to 5 days.In this case,it was found better to grow the algae first in HB No.6,plus the fertilizer at about half-dosage,after 3 days. Under these conditions,the algal concentration in mass culture could always be maintained above 400--500 mg./litre,irrespective of seasonal changes in the environment.The temperature, for instance,fluctuates between about 40℃.in summer and below 0° in winter.Annual yields are estimated at about 5 tons dry weight per rnou:75 tons/hectare,or 30 tons/acre.