microRNAs regulate gene expression levels. In cnidarian animals (sea anemones, corals, jellyfish and hydroids) microRNAs match their targets with nearly full complementarity in contrast to Bilaterian animals (Arthropods, vertebrates, nematodes...) where microRNAs match with a short sequence only. In this study, we test the complementarity requirements between microRNAs and their targets in the sea anemone Nematostella vectensis by injecting to Nematostella zygotes artificial microRNAs and characterizing their gene knockdown efficiency as well as their processing and loading into Argonautes, their carrier proteins.