We systematically investigate the optical properties of the InP1−x Bi x ternary alloys with 0 ≤ x ≤ 2.46%, by using high resolution polarized Raman scattering measurement. Both InP-like and InBi-like optical vibration modes (LO) are identified in all the samples, suggesting that most of the Bi-atoms are incorporated into the lattice sites to substitute P-atoms. And the intensity of the InBi-like Raman mode is positively proportional to the Bi-content. Linear red-shift of the InP-like longitudinal optical vibration mode is observed to be 1.1 cm−1/Bi%, while that of the InP-like optical vibration overtone (2LO) is nearly doubled. In addition, through comparing the Z(XX)Z̅ and Z(XY)Z̅ Raman spectra, longitudinal-optical-plasmon-coupled (LOPC) modes are identified in all the samples, and their intensities are found to be proportional to the electron concentrations.