The effect of glyphosate herbicide concentrations on the growth and some metabolic activities of the green alga Scenedesmus quadricauda and the blue-green alga (cyanobacteria) Merismopedia glauca isolated from soil (Assiut, Egypt) were assessed. The growth of Scenedesmus quadricauda and Merismopedia glauca was negatively affected by glyphosate herbicide. In addition, decreasing of the cell number as well as chlorophyll a, b and the dry weight of Scenedesmus were occurred with increasing the herbicide concentrations, while the dry weight and chlorophyll a of Merismopedia was increased by low concentration of glyphosate herbicide. The photosynthesis and respiration were increased in the two algae with increasing glyphosate herbicide. Increasing of soluble and insoluble carbohydrates with increasing of the herbicide in Scenedesmus. But in case of Merismopedia glauca the soluble sugars only were enhanced by all concentrations used of the herbicide. Decreasing soluble and insoluble proteins was occurred in Scenedesmus with increasing glyphosate. Also, glutelins, globulins and prolamines were decreased with increasing of glyphosate herbicide. The insoluble proteins, glutelins, globulins were increased and soluble proteins as well as prolamines were decreased with increasing of glyphosate herbicide to Merismopedia. Free amino acids were increased by increasing glyphosate herbicide in Scenedesmus and Merismopedia. Glyphosate herbicide inhibited the growth and some metabolic activities in the tested algae, this effect depend on the algal species, the type and concentration of the herbicide.