A single-phase red-emitting NaEu(MoO4)2 phosphor with nanosized particles was synthesized using a water-assisted solid state reaction (WASSR) method, a new low-temperature synthesis method developed by our group. NaEu(MoO4)2 exhibits a monoclinic structure with a space group C2/c (no. 15), which is composed of a Na/EuO8 dodecahedron with the site occupancy of Na/Eu = 1 : 1 and an MoO4 tetrahedron. To enhance the emission intensity of the NaEu(MoO4)2 phosphor, Gd3+ was doped into the Eu3+ sites and NaEu1-xGdx(MoO4)2 (0 < x ≤ 0.50) samples were synthesized using the WASSR method. The emission intensity of the phosphors was successfully enhanced by increasing the Gd3+ content in the samples with 0 ≤ x ≤ 0.30, but was reduced with x > 0.30. This indicates that the optimum composition of the phosphor for achieving a high emission intensity that is ∼3.8 times higher than that of the NaEu(MoO4)2 (x = 0) phosphor is NaEu0.70Gd0.30(MoO4)2. These phosphors exhibit a granular particle morphology with the particle size of the phosphor being ∼200 nm.