Due to the increasing burden of disease and demand for medicines, more and more pharmaceutical compounds are appearing in the environment. Toremifene (TOR), a first-line drug in the therapy of breast cancer, is widely used in the treatment of related diseases. However, the toxicity assessment of TOR is insufficient. Here, a model organism zebrafish and human umbilical vein endothelial cells (HUVECs) were used to investigate the effects and mechanisms of TOR on angiogenesis. The results showed that TOR exposure reduced hatching and survival rates, and increased the malformation rate. TOR inhibited angiogenesis by inducing nuclear condensation in zebrafish endothelial cells and impeding cell migration, resulting in vascular malformation in zebrafish embryos. TOR disrupted the cytoskeleton, suppressed HUVEC migration, adhesion, activity and division, induced cell cycle arrest, and accelerated apoptosis. qRT-PCR indicated that transcriptional levels of Integrin β1, Rho, ROCK, and MLC-1 reduced in the TOR-exposed groups, and western blot indicated that TOR decreased the contents of Integrin β1, Rho, ROCK, MLC, and pMLC in the Rho/ROCK signaling pathway. Collectively, TOR may disturb endothelial cell behaviors by disrupting the cytoskeleton via the Rho/ROCK signaling pathway, ultimately resulting in abnormal angiogenesis. The study increases awareness of the toxicity of TOR to aquatic organisms and raises public concern about the health risks posed by anti-tumor drugs.