AbstractAt present, no effective treatment exists for the clinical toxicity of cobalt nanoparticles (CoNPs, 30 nm) after metal-on-metal (MOM) artificial joint replacement. As such, a better understanding of the CoNPs-toxicity mechanism is necessary and urgent for the development of effective and safe detoxification drugs. Our purpose was to explore the role of bioactive nano-selenium (BNS, > 97%) in antagonizing the toxicity of CoNPs and its mechanism through the Keap1-Nrf2-ARE signaling pathway. To examine BNS detoxification, we exposed HUVEC cells to CoNPs and BNS for 24 h, before measuring cell activity, reactive oxygen species (ROS), the GSH level, inflammatory factors, and KNA signaling pathway-related transcript and protein expression. CoNPs stimulate intracellular inflammation and ROS production to bring about significant downregulation of cellular activity and the GSH level. Conversely, BNS reduces ROS generation and suppresses inflammatory factors within cells to reduce CoNPs-mediated cytotoxicity, possibly via the KNA signaling pathway. Based on our results, BNS antagonizes CoNPs toxic effects by suppressing ROS production through the KNA pathway. Our research provides new insight into the clinical treatment of CoNPs toxicity and explores the potential of BNS in detoxification therapy. Trial registration: no human participant.