A positioning device for positioning a number of two-sided adhesive pieces includes a base, a number of pulling blocks, and a pressing block. The base includes a positioning block defining a number of positioning holes. Each pulling block includes a connecting plate, and a supporting plate protruding out from a top end of the connecting plate. A first surface of each adhesive piece is adhered on a top surface of one of the supporting plate. The connecting plate is received in a corresponding one of the positioning hole. The pressing block is attached to the positioning block. A second surface of each adhesive piece to be adhered to a bottom surface of the pressing block.