Abstract: When designing microstrip antenna array, reducing the space between array elements can lead to mutual coupling increasing, which decreases the gain of antenna. In this letter, an efficient mutual coupling reduction method is in troduced for very closely spaced microstrip antennas. Through two simple coplanar waveguide (CPW) neutralization lines on the ground plane, the field inside the first element is guided to second element creating another path for mutual coupling, the phase and amplitude of which may be varied to neutralize the original existing mutual coupling between the elements. More than 21dB isolation ( |S21 |) is achieved with a very close distance of about 0. 024 0(edge-to-edge distance 0 , is free space wavelength) and 0. 38 (center-to-center distance). Radiation characteristic of array element is improved, the radiation pat tern of which is close to radiation pattern of a single patch. In order to validate the propose method, a two-element array based on it is designed and measured. Compared to a two-element array with the same size, the gain of the proposed array is improved by 1. 2dBi and compared to a two-element array with the same gain, the size is decreased by 10. 2% as well as a obvious improvement of side lobe.