Silver nanoparticles (AgNPs) have gained widespread use in medical, health, consumer and industrial applications. Given the increasing use of products containing AgNPs, an increase in the amount released into the environment is also expected. Therefore, it is of growing importance to study the effects of AgNPs on living organisms. The aim of this study was to investigate the potential toxicity of AgNPs on the larval development of sea urchin Paracentrotus lividus. For this purpose, the sea urchin embryonal development test (SUEDT) was used. Fertilised zygotes of P. lividus were exposed to concentrations of 50, 100 and 500 μg/L AgNPs and larval length was measured after 48 hours. Larvae treated with 50 and 100 μg/L AgNPs showed an increase in size and development rate compared to the control, while larvae treated with 500 μg/L AgNPs exhibited a reduced development rate and were significantly smaller in size compared to the control. Thus, the test has shown that AgNPs have toxic effects on the test species dependent on the dose administered. The stimulatory effects observed in larvae treated with lower concentrations of AgNPs could possibly be related to hormesis. However, further studies should be conducted in order to clarify the precise mechanisms that AgNPs and different abiotic factors (pH, dissolved oxygen, temperature, ammonia) simultaneously exert on larval development. In addition, further studies should aim to improve understanding of the ways AgNPs interact with fertilised eggs of P. lividus.