A compact 4-element multiple-input multiple-output (MIMO) antenna for terminal devices is proposed. The proposed antenna consists of 3 identical dipole antennas and 1 slot antenna, with 39 mm × 30 mm in size, operating at a high-frequency band of WIFI, 5.15 to 5.85 GHz. After a design procedure is executed, both simulated and measured results are obtained to demonstrate that the return loss of the presented MIMO antenna is more than 10 dB with isolation level better than 20 dB. The radiation efficiency is higher than 70%, and the gain is above 2.8 dBi.