In this article, alpha-NaYF4 nanocubes were synthesized with a simple and environmentally friendly method at room temperature. The structure and morphology of the products were characterized by X-ray diffraction and scanning electron microscopy. The influence of the F-/Y3+ molar ratio on the morphology of the products was examined. The products changed from spherical nanocrystals to cubic nanocrystals when the F-/Y3+ molar ratio gradually increased from 4:1 to 16:1, and excessive F- ions were necessary for the formation of regular NaYF4 nanocubes in our synthesis procedure. The formation process of these alpha-NaYF4 nanocrystals was traced via time-dependent experiments. Several nanometer-sized NaYF4 nanocrystals changed into 100 nm sized NaYF4 nanocrystals with prolonging of the reaction time. Additionally, the photoluminescence properties of Eu3+-doped samples were investigated. The excitation spectrum consists of the characteristic absorption peaks of Eu3+ corresponding to the direct excitation from the europium f-electrons. The charge-transfer band of Eu3+-F- is not present in our measured range. The D-5(0) -> F-7(1) transition is much stronger than the D-5(0) -> F-7(2) transition in our samples.