Abstract: Process for the production and extraction of thermostable super-oxide-dismutases from a photosynthetic microorganism cell. The thermostable superoxide-dismutase production and extraction process consists a) of culturing in the temperature range 40.degree. to 80.degree. C., in a closed photoreactor made from a light-transparent material and which is thermally resistant within said range, aerobic, photosynthetic, thermophilic microorganisms, which produce oxygen and grow exponentially in said range, said microorganisms being suspended in a culture medium and chosen from among microalgae and cyanobacteria and b) extracting from the culture medium the freshly produced, thermostable superoxide-dismutases, by cellular crushing, ultrafiltration and selective precipitation.