Ternary TlGaP and TlGaAs alloys, which are important constituent quaternary alloys of TlxIn1 - x - yGayP and TlxIn1 - x- yGayAs as new III-V compound semiconductors for long wavelength optical devices as well as temperature-insensitive wavelength laser diodes, are successfully grown by gas-source molecular beam epitaxy (MBE). Optical phonon modes of TIGaP and TlGaAs ternary alloys are investigated, for the first time, by Raman scattering measurement. The Raman spectra of TIGaP with larger Tl composition on GaAs substrate consist of four separate bands in the optical frequency range, GaP-like LO 393 cm(-1), GaP-like TO 357 cm(-1), TlP-like LO 346 cm(-1) and TlP-like TO 307 cm(-1), respectively. The GaAs-like phonon modes for TlGaAs on InP substrate are also observed. The results show an agreement between the Raman scattering measurements and X-ray diffraction experiments.