When Chlorella biomass was hydrolyzed in the presence of 2% HCl and 2.5% MgCl<SUB>2</SUB>, a sugar concentration of nearly 12%, and a sugar recovery of about 83% was obtained. Fermentation experiments demonstrated that glucose in the Chlorella biomass hydrolysates was converted into ethanol by Saccharomyces cerevisiae with a yield of 0.47gg<SUP>-1</SUP>, which is 91% of the theoretical yield. This chemical hydrolysis approach is thus a novel route for the hydrolysis of biomass to generate fermentable sugars.