ABSTRACTZnO NPs can adsorb onto soil particles and potentially enter groundwater. Nematodes and other soil microfauna are vital to the soil's health and nutrient cycles, yet they are seriously endangered by ZnO NPs. A dose–response study using Panagrellus redivivus was applied. The study evaluated the effects of ZnO NPs with sizes of 15 and 140 nm on various age groups (J2, J3‐J4 and adult) and sexes. After nematodes were exposed to varying ZnO concentrations, their survival was assessed 24 h later using a microplate setup. Males demonstrated increased mortality at higher concentrations of ZnO (15 nm), due to their size and morphological differences. As for the age groups, J2 larvae showed the lowest survival rate to ZnO NPs. However, the larger‐size ZnO NPs proved to be more toxic in the case of younger age groups and marginally more toxic in adult and female individuals due to their irregular shape and higher ion release. Our results highlight significant differences in survival to ZnO NPs based on nematode sex and age. Larvae (J2) were the most responsive, and the difference between the two applied compounds was the most visible there, suggesting the importance of involving various life stages in toxicity assessments.