Environmental barrier coating materials are widely applied on the surface of ceramic matrix composites in aero engines and hypersonic vehicles, primarily serving to isolate high-temperature water vapor and air. To ensure a sufficiently long service life, environmental barrier coating materials must possess characteristics such as high toughness, high hardness, and relatively low Young’s modulus. In this study, dense RETa3O9 (RE=La, Nd, Sm, Gd, Ho) tantalate ceramics were prepared by spark plasma sintering technology, and their nanomechanical properties were systematically investigated. The nanoindentation technique was employed to comprehensively characterize key mechanical properties of RETa3O9 ceramics, including hardness, Young’s modulus, fracture toughness, wear resistance and stiffness, while analyzing the main factors influencing these mechanical properties. The research results demonstrate that the Youngs modulus (166.72～196.70 GPa) and hardness (9.52～11.69 GPa) of RETa3O9 ceramics are mainly influenced by rare earth ion radius and density. The fracture toughness (1.44～1.82 MPa·m1/2) shows a strong correlation with grain size, and the RETa3O9 ceramics prepared by spark plasma sintering process exhibit finer grain size, which significantly enhances fracture toughness. The stiffness (186 064～285 730 N·m-1) and wear resistance (0.60～0.65) are primarily affected by the material’s hardness and Young’s modulus, with stiffness showing a positive correlation with hardness, while demonstrating overall excellent wear resistance. This study comprehensively evaluated the integrated mechanical properties of RETa3O9 ceramics through nanoindentation testing system, exploring their potential as environmental barrier coating materials. The results indicate that SmTa3O9 exhibits outstanding comprehensive mechanical properties, making it a highly promising candidate material for environmental barrier coatings.