To understand the effects of contamination of insecticides onphototrophs, and to determine the responses of these organisms against these chemicals are extremely important in understanding how the ecosystem is affected. Azadirachtin used as insecticide due to inhibiting growth of insects and preventing them feeding on plants and it contaminates to aquatic ecosystems. Azadirachtin effects to a phytoplanktonic organism as called Arthrospira platensis and creates oxidative stress in their cells.