Abstract Orthorhombic In₃B₅O₁₂ was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 12.2 GPa and 1500°C. Its structure is isotypic to the rare earth analogs RE ₃B₅O₁₂ (RE=Sc, Er–Lu). In the field of indium borate chemistry, In₃B₅O₁₂ is the third known ternary indium borate besides InBO₃ and InB₅O₉. The crystal structure of In₃B₅O₁₂ has been determined via single-crystal X-ray diffraction data collected at room temperature. It crystallizes in the orthorhombic space group Pmna with the lattice parameters a=12.570(2), b=4.5141(4), c=12.397(2) Å, and V=703.4(2) ų. IR and Raman bands of In₃B₅O₁₂ were theoretically determined and assigned to experimentally recorded spectra.