The thermoelastic parameters of Ca₃Cr₂Si₃O₁₂ uvarovite garnet were examined in situ at high pressure up to 13GPa and high temperature up to 1100K by synchrotron radiation energy-dispersive X-ray diffraction within a 6-6-type multi-anvil press apparatus. A least-square fitting of room T data to a third-order Birch–Murnaghan (BM3) EoS yielded K₀ = 164.2±0.7GPa,V₀ = 1735.9±0.3 ų (K’₀ fixed to 4.0). P–V–T data were fitted simultaneously by a modified HT-BM3 EoS, which gave the isothermal bulk modulus K₀ = 163.6±2.6GPa, K’₀ = 4.1±0.5, its temperature derivative (∂K_0,T/∂T)_P =–0.014±0.002 GPa K⁻¹, and the thermal expansion coefficients a₀ = 2.32±0.13 ×10⁻⁵ K⁻¹ and b₀ = 2.13±2.18 ×10⁻⁹ K⁻² (K’₀ fixed to 4.0). Our results showed that the Cr³⁺ enrichment in natural systems likely increases the density of ugrandite garnets, resulting in a substantial increase of mantle garnet densities in regions where Cr-rich spinel releases chromium through a metasomatic reaction.