A sifting device for workpieces includes a box, an electric cabinet, a sifting assembly, an air blower, and an collector. The box receives the workpieces. The sifting assembly is received in the box, and includes a baffle and a guiding board, the guiding board defines a plurality of gaps, and a slit is formed between the baffle and the guiding board, and communicates with the plurality of gaps. The air blower is directed by the electric cabinet and communicates with the gap to adjust a direction of the workpieces to allow the workpieces to pass through the gap and the slit. The collector communicates with the slit to output the workpieces.