The chemical composition, nutritional and toxicological evaluation of Nannochloropsis sp. were determined. The algal biomass was produced in a 63 L, 4 cm diameter fotobioreactor under outdoor conditions was enriched sea water medium. Its chemical composition was (g/100 g): proteins 40, lipids 25.5, crude fiber 5, N.N.E. 11.5, ash 10. The most abundant relative fatty acids were (g/100 g): palmitic 23, palmitoleic 24.5 and eicosapentaenoic 23. The aminoacid content of the algal protein was higher than the FAO/WHO 1981 standard. The mineral content revealed an absence of bioconcentration of toxic elements. The nutritional and toxicological effects of the intake of biomass were evaluated in growing rats. Animals were fed diets containing 0% (Control), 5% or 10% (w/w) Nannochloropsis sp. for 2, 3 or 4 weeks (n=6 per group). Its intake did not affect body growth, organs wieght or haematological parameters. Only serum cholesterol (total and HDL) were higher in rats fed supplemented diet. The results of this study indicate the lack of toxicity of the biomass.