An electronically reconfigurable reflectarray antenna of 12 × 12 units is presented in this paper. The element consists of a slotted square patch and a gapped metal square ring. PIN diodes are loaded on slotted square patches, which can be electronically controlled to produce two states with 180˚ phase difference. A reflectarray prototype is fabricated and experimentally studied. Experimental results agree well with the full-wave simulations by Ansys HFSS, and scanning beams within ±45˚ range are obtained with a maximum aperture efficiency of 14.9% at 5.8 GHz. 1-dB bandwidth is 9.9%, and 3-dB bandwidth is 19.1%.