A wideband microstrip patch antenna (MPA) with a pair of square open-loop resonators is proposed. Initial, a low-profile U-slot MPA with the conventional aperture-coupled feeding is designed. The second resonant mode is excited around the fundamental mode of the MPA due to the introduced U-slot on the radiating patch. Then, by employing a square open-loop resonator on the feeding line, the antenna achieves an addition resonant mode around its original modes. After that, an identical square open-loop resonator is further added for the bandwidth enhancement. In final, the proposed MPA is simulated and studied. The results illustrate that the impedance bandwidth of the antenna with two square open-loop resonators is successfully extended to about 10.72%, while keeping a low profile of about 0.04 λ (λ is the free-space wavelength). Meanwhile, a stable gain varied from 4.63 to 7.88 dBi is acquired within the whole operating band.