A reconfigurable millimeter-wave (28/38 GHz) antenna is proposed for future generations of mobile communication. The antenna is constructed as dual-slot on substrate integrated waveguide (SIW) cavity. The two slots are parallel and cut in the upper wall of the SIW cavity. This antenna is reconfigurable and can operate at either 28 or 38 GHz by a rotary strip. This strip can be rotated while touching the external surface of the upper wall of the SIW cavity by means of a micro-electro-mechanical system (MEMS) servomotor. When the rotary strip is rotated to be perpendicular to the axis of symmetry of the antenna and feeding line (i.e. parallel to the slots) it operates at 28 GHz. When the rotary strip is rotated to be aligned with the axis of symmetry (perpendicular to the slots) the antenna operates at 38 GHz. In latter case, each slot is divided into two slots to form four radiating slots of the same length. The dual-slot antenna structure enhances the radiation efficiency at both 28 and 38 GHz. The antenna has impedance matching bandwidths of 1.1GHz and 0.9 GHz about the center frequencies 28 and 38 GHz, respectively. The values of the maximum gain produced at 28 and 38 GHz are 5.4 and 6 dBi, respectively. The corresponding radiation efficiencies are 80.5% and 82%, respectively. For experimental validation of the simulation results, a prototype is fabricated for the proposed antenna. The measurements and simulation results agree well with each other.