We have performed polarized and temperature-dependent Raman scattering measurements on extremely large magnetoresitance compounds TaAs_2 and NbAs_2. In both crystals, all the Raman active modes, including six A_g modes and three B_g modes, are clearly observed and well assigned with the combination of symmetry analysis and first-principles calculations. The well-resolved periodic intensity modulations of the observed modes with rotating crystal orientations, verify the symmetry of each assigned

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... mode and are fitted to experimentally determine the elements of Raman tensor matrixes. The broadening of two A_g modes seen in both compounds allows us to estimate electron-phonon coupling constant, which suggests a relatively small electron-phonon coupling in the semimetals TaAs_2 and NbAs_2. The present study provides the fundamental lattice dynamics information on TaAs_2 and NbAs_2 and may shed light on the understanding of their extraordinary large magnetoresistance.