This article presents a miniaturized octa-port high gain multiple-input-multiple-output (MIMO) antenna loaded with an electromagnetic band gap (EBG) layer for the use in 5G wireless communication applications. Each resonator of the presented antenna consists of a rectangularlike patch with truncated side edges and a partial ground plane. A layer of EBG unit cells is introduced underneath the antenna elements to increase the gain and restrain the surface wave effects, obtaining improved isolation amongst the resonating elements. The −10 dB impedance bandwidth of the prospective antenna with EBG is 12 GHz (21-33 GHz), and it provides isolation of > 28 dB. The peak gain of the EBG-backed antenna is 17 dB. The presented mm-wave MIMO antenna offers decent diversity proficiency metrics like envelope correlation coefficient (< 0.36), diversity gain (∼ 10 dB), and total active reflection coefficient (−24.75 dB). The overall size of the octa-port MIMO antenna is 27.2 mm × 27.2 mm. The presented MIMO antenna could be used for n257/n258/n261 mm-wave bands.