en Toxicology Toxicology پژوهشي Orginal research papers <span style="font-size:12pt"><span new="" roman="" style="font-family:" times="">This paper aims to investigate the biological and cytotoxic characteristics of venoms extracted from <i>Rhopilema nomadica</i> and <i>Chrysaora hysoscella</i> jellyfish collected from the Persian Gulf. The cytotoxic effect of the venoms is surveyed on human fibroblast skin cells (HU02) using the The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Moreover, the protein molecular weight was determined and the toxicity test (LD50) of venoms were explored on BALB/c mice. The <i>R. nomadica</i> venom possessed a higher protein concentration with the lowest molecular weight protein via SDS-PAGE (12.5 %) along with more peaks obtained by HPLC. In addition, the results of both LD50 and MTT are affected by the venom characteristics. Besides, intravenously and intraperitoneally LD50 were 1.26 and 2.35 for <i>C. hysesella</i> and 0.65 IV and 1.6 IP for <i>R. nomadica</i>, respectively, suggesting that <i>R. nomadica</i> venom was more lethal. The results of the MTT assay on Hu02 fibroblast cells for 24 h revealed that <i>R. nomadica</i> had more lethal effects on skin cells compared to <i>C. hysoscella</i>. Escherichia coli, whereas methicillin-resistant Staphylococcus aureus had no antibacterial activities in the presence of both <i>R. nomadica</i> and <i>C. hysoscella</i> venoms. Meanwhile, the venoms had antibacterial effects on Pseudomonas aeruginosa and S. aureus, which were still weak compared to the other reported species. Overall, <i>R. nomadica</i> venom was more lethal in the case of mice and human skin cells and likely with more symptoms in prey. Finally, considering the relatively high viability of different bacteria in diverse dilutions of venom, it seems that victims not only should face dermal injuries and possible scars caused by direct stings but also the presence of venomous protein on the dermal tissue may provide a cultivation medium for different kind of bacteria.</span></span> Bacterial viability rate, Bradford assay, Human fibroblast skin cells [HU02], Jellyfish venom, MTT assay 171 195 http://jifro.ir/browse.php?a_code=A-10-4829-1&slc_lang=en&sid=1 S. Ketabdari s_ketab2012@yahoo.com 100319475328460051284 100319475328460051284 No Department of Marine Biology, Faculty of Marine Science and Oceanography, Khorramshahr Marine Science and Technology University, Khorramshahr, Iran, P.O. Box: 34619-64199 H. Zolgharnein zolgharnein@kmsu.ac.ir 100319475328460051285 100319475328460051285 No Department of Marine Biology, Faculty of Marine Science and Oceanography, Khorramshahr Marine Science and Technology University, Khorramshahr, Iran, P.O. Box: 34619-64199 H.R. Goudarzi niknamfar@yahoo.com 100319475328460051286 100319475328460051286 Yes Research and Development Department, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran; P.O. Box: 3197619751 A. Savari savari53@yahoo.com 100319475328460051287 100319475328460051287 No Department of Marine Biology, Faculty of Marine Science and Oceanography, Khorramshahr Marine Science and Technology University, Khorramshahr, Iran, P.O. Box: 34619-64199 Z. Salehi Najaf Abadi zahra.salehi@live.com 100319475328460051288 100319475328460051288 No Research and Development Department, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran; P.O. Box: 3197619751