en Toxicology and polution Toxicology and polution پژوهشي Original research papers Recently nanoparticles, particularly silver nanoparticles, are broadly used in industry, hence the contamination of the environment with AgNPs has caused considerable concern. In this study, the toxicity of biosynthetic nanosilver produced by two macroalgae: <em>Sargassum boveanum </em>and<em> Ulva flexuosa</em> extracts were compared with chemical nanosilver in <em>Daphnia magna</em>. Size and quality of nanoparticles evaluated by TEM, FT-IR spectrum, and Particle size analyzer. The acute toxicity test was evaluated following the OECD and Test guideline No: 211. <em>D. magna</em> were reproduced using parthenogenesis from a single individual according to OECD guideline. Then <em>Daphnia </em>exposed to eight serial dilutions of each nanosilver in triplicates for 48 hours. The mortality rate after 12h, 24h, 36h, and 48h were recorded and analyzed using probit software. Results showed that all nanosilver (regardless of their synthesis origin) were toxic in Daphnia and acute toxicity of this nanosilver was different (p<0.05).&nbsp; The 48h LC₅₀ of SPN, UPN, and CPN in Daphnia were 1.03, 3.24 and 0.03 mg L^-1 respectively. The mortality rate in <em>D. magna</em> enhanced in all tested groups, along with increasing nanosilver concentration and exposure time duration. Highest toxicity belongs to chemical nanosilver (LC₅₀ = 0.03 mg L^-1), which was 30 and 100 times more toxic than SP (LC₅₀= 1.03) and UP (LC₅₀ = 3.24 mg L^-1) respectively. According to the high toxicity of chemosynthetic nanosilver compare to biosynthetic ones, biosynthetic nanoparticles are highly recommendable and environmentally friendly alternative to chemical oriented nanoparticles. <div><br> &nbsp;</div> Nanosilver, Daphnia magna, Sargassum boveanum, Ulva flexuosa, Biosynthetic 74 85 http://ijaah.ir/browse.php?a_code=A-10-148-1&slc_lang=en&sid=1 Z Tulaby Dezfuly زهرا طولابی دزفولی z.tulaby@gmail.com 10031947532846001652 10031947532846001652 No Shahid Chamran University of Ahvaz دانشکده دامپزشکی دانشگاه شهید چمران اهواز M Alishahi مجتبی علیشاهی alishahim@scu.ac.ir 10031947532846001653 10031947532846001653 Yes Department of Clinical Sciences Faculty of veterinary, Shahid Chamran University of Ahvaz, Ahvaz, Iran گروه علوم درمانگاهی دانشکده دامپزشکی دانشگاه شهید چمران اهواز A Aramoon امیر آرامون araamoon.haser@gmail.com 10031947532846001654 10031947532846001654 No Shahid Chamran University of Ahvaz, Ahvaz, Iran دانشکده دامپزشکی دانشگاه شهید چمران اهواز S Mashjoor سکینه مشجور sakynemashjoor@gmail.com 10031947532846001655 10031947532846001655 No Department of Marine biology, Faculty of Marine Science and Technology, Hormozgan University, Bandar Abbas, Iran Department of Marine biology, Faculty of Marine Science and Technology, Hormozgan University, Bandar Abbas, Iran