The phonon mode(s) controlling the multiphonon relaxation (MPR) in PbO-Bi2O3-Ga2O3 glass was analyzed, and the effect of GeO2 addition on the MPR process was investigated. MPR rates were obtained from the lifetimes of the TM3+:H-3(4) level in glasses over the temperature range 20-280 K. In PbO-Bi2O3-Ga2O3 glass, phonons from the bending vibration between GaO4 tetrahedra (similar to550 cm(-1)) controlled the MPR process. On the addition of GeO2, the phonon mode at similar to770 cm(-1) due to the stretching vibration of GeO4 tetrahedra started to affect the MPR process. Phonon modes controlling the MPR process in PbO-Bi2O3-Ga2O3-GeO2 glass were both 550 cm(-1) and 770 cm(-1).