The AgIAg2MoO4Ag2PO3.5 glasses were prepared and their silver ion conducting properties and structure investigated. For the glasses with a constant AgI content and involving two types of oxoacid salt, Ag2MoO4 and Ag2PO3.5, an enhancement of the conductivity at 298 K was observed in the range y = 0.6−0.8, where y denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms included in the glasses, y = [P]([P] + [Mo]). 31P magic angle spinning (MAS) NMR spectra suggest that, with decreasing y, the number of Q0 units (monomeric units with no bridging oxygen atoms) increased, while that of Q1 units (terminal units with one bridging oxygen combined with another P atom) decreased. The number of Q1 - Mo units (terminal units with one bridging oxygen connected to a Mo atom) showed a maximum in the range y = 0.6−0.8. The position of the maximum in the number of Q1 - Mo units was nearly the same as that of the maximum in the conductivities of the glasses. This agreement suggests that the Q1 - Mo structural unit is closely related to the enhancement of conductivity of the glasses.