Raman measurements between 77°K and 296°K are reported for the superionic conductor RbAg4I5. Careful attention is paid to the temperature region of the two phase transitions at 121°K and 208°K. We can detect no shifts in any of the numerous phonon modes except one at 22.9 cm-1, which abruptly and reversibly appears in the lowest temperature phase. Raman results for the isomorphic material KAg4I5 are the same with the same mode appearing in the low temperature phase. Thus, the results in these systems are markedly different from those in AgI, where there are very large changes at the superionic conducting transition temperature. © 1976.