Rare earth elements are integral to modern technology, but their increasing environmental distribution due to anthropogenic activities poses potential health risks to humans. This study utilized zebrafish as a model to assess developmental and locomotor performance effects of europium and samarium. Exposure to Eu or Sm induced a reduction in heart rate, growth inhibition, and morphological deformities. RNA-Seq revealed gene expression alterations linked to critical biological processes and functions following Eu or Sm exposure. Impaired organogenesis in liver and exocrine pancreas, evident through fluorescence imaging, was confirmed transcriptionally. Exposure to Eu or Sm significantly impaired the burst and spontaneous swimming behaviors of zebrafish larvae, characterized by pronounced reductions in movement distance, frequency, and velocity. These observations indicate severe locomotor dysfunction in zebrafish exposed to Eu and Sm. The comprehensive downregulation of the oxidative phosphorylation pathway is likely a primary factor contributing to these motor impairments. Apoptosis induced by Eu and Sm, confirmed through acridine orange staining, was accompanied by the upregulation of the intrinsic apoptosis pathway. Our findings contribute critical insights into the health risks of rare earth elements, informing risk assessment and management strategies.