The subsolidus region of the Ag2MoO4-MgMoO4-In2(MoO4)3 ternary salt system has been studied by X-ray powder diffraction. The formation of new compounds Ag1 − xMg1 − xIn1 + x(MoO4)3 (0 ≤ x ≤ 0.6) and AgMg3In(MoO4)5 has been established. The unit cell parameters of solid-solution samples have been determined. The Ag1 − xMg1 − xIn1 + x(MoO4)3 phase of variable composition has a NASICON-type structure (space group R\( \bar 3 \)c) AgMg3In(MoO4)5 is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P\( \bar 1 \), Z = 2) with the following unit cell parameters: a = 7.0374(5) A, b = 17.932(1) A, c = 6.9822(4) A, α = 87.309(6)°, β = 100.832(6)°, γ = 92.358(6)°. The compounds Ag1 − xMg1 − xIn1 + x(MoO4)3 and AgMg3In(MoO4)5 are thermally stable up to 960 and 1030°C, respectively.