Uniform and well-crystallized tetragonal NaGd(MoO4)(2) nanocrystals with the morphology of nanocubes were synthesized via a modified hydrothermal synthesis method with oleic acid as complexing agent. The assynthesized NaGd(MoO4)(2) nanocubes were characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction respectively. The side-length of the NaGd(MoO4)(2) nanocubes is about 100-150 nm. The SAED pattern indicates highly crystalline nature of the NaGd(MoO4)(2) nanocubes. The effect of Na2MoO4 contents on the formation of NaGd(MoO4)(2) nanocrystals is investigated. A possible growth mechanism of NaGd(MoO4)(2) nanocubes is deduced based on time-dependent morphology evolution and XRD analysis. Down-shifting/ upconversion photoluminescence properties of NaGd(MoO4)(2): Eu3+, Tb3+ and Yb3+/ Er3+ nanocubes are investigated in detail. Furthermore, the energy transfer mechanism for upconversion luminescence in NaGd(MoO4)(2): Yb3+/ Er3+ nanocubes is investigated on the basis of energy level scheme and the excitation power dependence of upconversion luminescence intensities.