Elementary composition of humic acids from 11 freshwater lake sediments was determined with the following results. 1) Carbon content (%): Soil (57.9)>Marine (52.3)〜Lake (51.9) Atomic H/C ratio: Marine (1.42)>Lake (1.31)>Soil (0.98) Atomic N/C ratio: Lake (0.087)>Marine (0.058)〜Soil (0.055) In elementary composition, humic acids of lake sediments resemble those of marine sediments rather than soils. This indicates a close relation of the constitution of humic acid to source materials and environmental condition of its formation. 2) The H/C and N/C ratios of humic acids from lake sediments, decrease with increase in their carbon content. And there exists a relationship between H/C ratio and absorbance at 600 mμ of humic acid. These regularities are essentially identical with those already observed for soil humic acids.