To characterize the microstructure, hardness, and fracture toughness of yttria-partially stabilized zirconia ceramics and to evaluate the effect of thickness on their biaxial flexural strength (quasi-static and fatigue tests). Disc-shaped specimens (12 mm in diameter, 1.2 mm-thick) were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST), and 5Y-PSZ (Vita YZ XT) ceramics. The samples had their crystalline phases, microstructure and composition analyzed with X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). A microhardness tester was used to assess the Vickers hardness and fracture toughness of each material. Thinner discs were also prepared to evaluate the thickness effect (0.7 or 1.2 mm) on the biaxial flexural strength. The monotonic biaxial flexural strength tests were performed according to ISO 6872/2015. The same test set up was used to perform fatigue tests (incremental steps of 25 MPa for 10,000 cycles starting from 400 MPa). SEM images revealed surface defects on 4Y-PSZ and 5Y-PSZ samples, while 3Y-TZP exhibited greater grain uniformity. All ceramics showed similar chemical compositions. The main difference was the amount of yttria, which was higher in 5Y-PSZ, followed by 4Y-PSZ, and 3Y-TZP. The same trend was observed regarding the amount of cubic phase (5Y-PSZ > 4Y-PSZ > 3Y-TZP). 5Y-PSZ and 3Y-TZP presented the highest hardness values (1529.8 152.6 and 1421.5 109.7, respectively). The highest fracture toughness was observed in 3Y-TZP (5.66 0.56), while 4Y-PSZ (4.44 0.58) and 5Y-PSZ (4.29 0.38) showed similar values. The lowest flexural fatigue strength was observed in 5Y-PSZ (0.7 mm: 376.7 MPa and 60.3 ×103 cycles for failure, 1.2 mm: 440 MPa and 73 ×103 CFF), while 3Y-TZP and 4YSZ were statistically similar (3Y 0.7 mm: 520 MPa and 89 ×103 CFF, 1.2 mm: 516.7 MPa and 88.3 ×103 CFF, 4Y 0.7 mm: 603.3 MPa and 105.6 ×103 CFF, 1.2 mm: 546.6 MPa and 94.3 ×103 CFF). Comparing the monotonic and fatigue tests, 3Y-TZP suffered the highest (1.2 mm: 47.04%) and lowest (0.7 mm: 29.85%) percentage of degradation. 5Y-PSZ degraded more than 4Y-PSZ (5Y 0.7: 46.38%, 1.2: 41.38%, 4Y 0.7: 35.19%, 1.2: 38.52%). Despite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.