In this study, the lethal concentration and acute toxicity of silver nanoparticles synthesized using seaweed Sargassum angustifolium that is produced by biological methods were investigated at static renewal condition during 96 hours in common carp in accordance with standard methods OECD. TEM analysis showed that the average size of the bio nanoparticles were found to be 32.54 nm and spherical in shape. Since the exact amount of lethal concentration of this silver nanoparticle has not been determined in fish previously, at first determining the lethal concentration range, then the preliminary experiments was carried out at several concentrations. Once the lethal concentration, LC50 tests were done at different concentrations. The results showed that the LC50 at 24, 48, 72 and 96-h after exposure were 79.54 ± 0.007, 52.17 ± 0.006, 30.62 ± 0.008 and 11.34 ± 0.016 mg/L respectively. According to these results, the mortality rates of common carp showed an increasing trend with increasing concentration and exposure time, that is indicating the toxicity of biological synthesized AgNP in high concentration for common carp.