A complete Raman vibrational analysis has been performed on phase-pure rhombohedral phosphorus pentoxide (P4O10)) at room temperature. The "molecular" T-d symmetry is reduced to C-3, symmetry when bound in the rhombohedral crystalline lattice. Therefore. the 15 fundamental modes of vibration irreducibly represented as Gamma(vib) = 3A(1) + 3E + 3T(1) + 6T(2) reduce to 21 fundamental modes with a factor group analysis resulting in Gamma(vib) = 9A(1) + 12E for the irreducible representation, all of which are Raman active. Complete vibrational assignments and relative intensities. including all T, to E and A, splittings, are reported, Five new E fundamentals (262. 329 419, 829. and 846 cm(-1)) in the C-3nu, symmetry were observed. All peaks show good agreement with theoretical calculations.