Nanoparticles made from rare earth elements (REEs) have attracted significant attention due to their distinct quantum properties, surpassing the capabilities of larger rare earth materials. These exceptional characteristics make them ideal for a wide array of applications, particularly in sensor and biomedical applications where their remarkable nanomaterials attributes shine. Consequently, conducting thorough research, development, synthesis, and analysis of these rare earth nanoparticles is crucial. This chapter offers a comprehensive exploration into the nanomaterial advancements involving rare earth nanoparticles, encompassing their production techniques, characterization, electrochemical traits, and their application within various sensors to identify various biomolecules and hazardous substances. The examination also delves into how the size of the nanoparticles and modifications to the electrode surface impact their electrochemical performance. Moreover, it highlights the sensing mechanisms, selectivity, sensitivity, linear range, and detection limits of these sensors. Herein, the chapter underscores the highly sensitive nature of the explored methods, emphasizing their potential for precise and accurate identification of target substances. The broad spectrum of potential applications for detecting diverse biomolecules and hazardous materials is underscored, demonstrating the adaptability and significant potential of nanoparticles derived from rare earth elements across multiple domains. The insights provided in this section furnish a valuable source for future research endeavors, offering a glimpse into the present research status and the potential directions within the realm of rare earth element nanoparticles and electrochemical nanosensors.