A number of experimental studies on crystal growth have been performed in connection with a variety of crystalline systems ranging from simple oxides to complex organic compounds. In contrast, little is known regarding how crystals evaporate. By using a combination of real-time high-resolution electron microscopy at high temperature, image simulations, and density functional theory calculations, we demonstrate the evaporation of metal-phosphate nanocrystals with flat surfaces at atomic resolution. In situ imaging and direct comparison with image simulation results reveal that, while a layer-by-layer lateral process is macroscopically maintained, the cations preferentially evaporate over the (PO4)(3-) tetrahedral anions from shrinking ledges. The present observations provide the first atomic-scale experimental details of the evaporation of complex oxides, emphasizing the value of direct visualization in real time.