 Nanosymes are a new generation of artificial enzymes that have unique properties compared to natural counterparts such as stability in harsh environments, low cost, and ease of production and modification. Tumor catalytic therapy mediated by the generation of reactive oxygen species, ROS, has made great progress mainly from the peroxidase-like activity of nanosymes. Fe3O for nanosymes are the earliest type of nanomaterial discovered to possess peroxidase-like activity and have consequently received wide attention for tumor therapy due to its ROS generation ability and tumor cell killing ability. However, inconsistent results of cytotoxicity were observed between different reports, and some even showed the scavenging of ROS in some cases. Surface modification of Fe3O for nanosymes plays an important role in its therapeutic effects. This review will go over the fundamental catalytic mechanisms of Fe3O for nanosymes in recent advances in tumor catalytic therapy and discuss the importance of surface modification. Employing Fe3O for nanosymes as an example, we hope to provide an outlook on the improvement of nanosyme-based anti-tumor activity. This article was authored by Guo Hengtang, Zhu Yangyi, Zhu Wenliu, and others. We are article.tv, links in the description below.