Nanoplastics are produced abiotically and biotically from larger pieces of plastic. Although nanoplastic toxicity has received more attention recently, its biological effects have not been adequately investigated. In this study, the toxicity of nanoplastics (NPs) with an average size of <80 nm was carried out in the larvae of Artemia nauplii, an indicator organism of the aquatic environment, according to the OECD guideline 202 protocol. As a result, depending on exposure durations (24-96 h) and concentrations (50-300 μg/mL), the survival rate of nano-HDPE treated larvae was significantly reduced (p < 0.05). The larvae took up and internalized nano-HDPE at a concentration of 99.74 µg/mL, which is the calculated LC50 value. There was also a significant increase in biochemical markers in larvae at LC50 (p < 0.05). However, it was observed that this caused oxidative stress, cell membrane damage, limb loss and malformation in larvae treated with nano-HDPE.