Manganese-doped zinc phosphate (MnZP) glasses were prepared in Ar and air to examine the relationship between the physical properties and preparation atmosphere. The glass transition temperatures of these MnZP glasses were almost the same regardless of the preparation atmosphere. Although the absorption spectra of the 15 mol%-doped MnZP glasses prepared in different atmospheres exhibited significant differences, only small differences in the absorption tail were observed in the other MnZP glasses with lower Mn concentrations. It was found that the Mn K-edge X-ray absorption fine structure (XAFS) spectra of these glasses were also the same, indicating that the average local coordination states of Mn cations were similar in the concentration range considered. The quantum efficiency of the 15 mol%-doped MnZP glass prepared in air was lower than that of the glass prepared in Ar owing to the high absorption in the visible region of the former. It is expected that (NH4)2HPO4, which is the starting material for P2O5, prevents the oxidation reaction of Mn2+ during melting in air.