Nanometer oxides are widely used in medical, food and cosmetics. The widespread usage of nanoparticles may have hazardous consequences on numerous organisms. Thus, it is necessary to assess their fate in the environment. The environmental toxicity of nano iron oxides ( Fe 2 O 3 NPs) in several concentrations (50, 100, 200, 400, 800, 1000, 1200, 1400, 1600) mg/L on algal growth Klisinema persicum was evaluated by assessing some photosynthetic pigments, pH, oxygen content and cellular DNA damage (genotoxicity), using Comet assay through some indicators. This includes eight parameters (olive tail moment, %DNA in tail, tail moment, tail length, head diameter, comet area, comet height, as well as comet length) that were assessed for each comet on each slide in which the average values were recorded. Upon rising the concentrations of Fe2O3 NPs, the treatment outcomes with Fe2O3 NPs revealed a definite influence on a photosynthetic pigment (carotenoids and chlorophyll). In addition, with increasing concentration of iron oxide NPs, the acidity increased, while the oxygen content of the culture medium decreased. Genotoxicity was also increased in all parameters of comet assay with increased concentrations of iron oxide NPS and a higher increase of genotoxicity with a significant effect (P<0.05) documented at 1600 mg/L of iron oxide NPs, compared to the molecular characteristics in the control group. This was evidence that the high values of Fe2O3 NPs have a destructive effect resulting in DNA degradation and inhibiting the growth of algae.