A novel compact dual-band reconfigurable square-ring microstrip antenna is presented. The tuning is achieved using a single varactor diode connected to a small square patch attached to an inner corner of the square-ring. The square patch perturbs the symmetry and splits the two degenerate modes to create dual-band operation. The frequency ratio in the range of 1.04 to 1.4 can be achieved by the proper selection of the square patch size. The lower resonance frequency can be further decreased by loading the square patch at its corner by a reverse biased varactor diode.