Accurate force measurement is of great importance in both biological detection and physical processes. Optical tweezers have emerged as a vital tool for non-contact force detection, with nanometer-sized trapping probes playing a critical role in achieving high spatial resolution and force sensitivity. However, smaller nanoparticles with low refractive indices often result in reduced trapping forces, making optical trapping of nanoparticles for sensing a significant challenge. Recently, upconversion nanoparticles (UCNPs) have emerged as a promising new class of nanoprobes. These particles exhibit much higher trap stiffness compared to traditional gold nanoparticles of the same size. Furthermore, UCNPs offer stable and bright fluorescence, enabling fluorescence-based video trapping and precise force sensing. Leveraging their unique properties, such as surface modification and lanthanide ion emission, trapped UCNPs can also function as sensors for temperature and pH, broadening their application potential. These distinctive advantages make UCNPs an exceptional multifunctional probe for optical tweezers. This chapter provides an in-depth discussion on nanoparticle trapping, the mechanisms and benefits of UCNPs, and their applications in UCNP-based optical tweezers, which are poised to create novel opportunities in scientific research.