The toxic effects of glyphosate herbicide on growth, photosynthesis, chlorophyll and amino acids contents by the fresh water green alga Chlorella kessleri, were determined. The lower concentrations 5 and 10 mM were not severely toxic to the alga. However, the higher concentrations 15 and 20 mM exerted more toxicity effects. Algal growth, photosynthetic activity and chlorophyll contents were not affected severely by low concentrations, while high concentrations (20 mM), inhibited growth parameters by about 50%. The addition of the aromatic amino acids, phenyl alembic, tryptophane and tyrosine to the growth media recovered the growth by about 34% during the incubation period. The amino acids content of the control, 20 mM-treated and 20 mM-treated in addition to the aromatic amino acids were estimated and compared. The results also showed that the addition of the aromatic amino acids to the alga treated with 20 mM glyphosate, recovered the biosynthesis of the aromatic amino acids and also the other amino acids.