We report a facile and low-cost wet chemical method for preparation of gold (Au) nanocrystals with morphology of well-defined rhombic dodecahedron (RD). The Au nanocrystals with the RD shape have been synthesized by reducing HAuCl4 in N,N-dimethylformamide (DMF) solvent in an autoclave for 15-24 h at 90 degrees C. Thus-synthesized Au nanocrystals have been characterized by a scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). The results show that the RD nanocrystals are exclusively enclosed by twelve {110}-type facets. Furthermore, concave RD Au nanocrystals can also be produced only by changing reaction time or adding ascorbic acid (AA). A possible evolution mechanism of the RD Au nanocrystals has been suggested.