Glasses of various compositions were prepared in the systems AgI-Ag2MoO4-Ag3PO4 and AgI-Ag2MoO4-Ag2PO3.5; their silver ion conductivities were measured and the structures of constituent oxoanions were investigated by P-31 MAS-NMR. In the AgI-Ag2MoO4-Ag3PO4 glasses with a constant AgI content, the conductivities linearly changed with the composition parameter y = [P]/([P] + [Mol]), which denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms in the glasses. It was found from P-31 MAS-NMR spectra that the framework structure of the oxoanions : MoO42- and and PO43- did not change by mixing two kinds of oxosalts Ag2MoO4 and Ag3PO4. On the other hand, in the system AgI-Ag2MoO4-Ag2PO3.5 a distinct enhancement of conductivity was observed by mixing two kinds of oxosalts, Ag2MoO4 and Ag2PO3.5, at around the composition parameter y = 0.6-0.8 for the glasses with a constant AgI content. P-31 MAS-NMR spectra revealed that the framework structure of the oxoanions was changed by mixing two kinds of oxosalts Ag2MoO4 and Ag2PO3.5. The amount of Q(1-Mo) unit, which was a terminal unit with one bridging oxygen combined with a Mo atom, showed a maximum at around y = 0.6-0.8. These results suggest that the conductivity enhancement by mixing two kinds of oxosalts is related to the structural change of oxoanions forming framework structure of the glasses and that the appearance of the structural unit Q(1-Mo) is closely related to the conductivity enhancement in the glasses.