In this paper, an integrated design with a multiple-input multiple-output (MIMO) antenna system for fourth generation (4G) and fifth generation (5G) applications is presented. The proposed design contains a two-element slotbased MIMO antenna system for 4G and a connected antenna array (CAA)-based two-element MIMO antenna system for a potential 5G band. Two rectangular loops are etched on the periphery of the ground plane. The top and bottom portions of the thin loops act as the two 4G MIMO antennas, while parts of their sides are acting as 5G arrays. The antenna system is fabricated on a commercially available Roger 4350 substrate with ϵrequal to 3.5, while the dimensions of the board are 100 × 60 × 0.76 mm3representing a typical smart phone back plane size. The integrated antenna system covers multibands at 4G with a combined bandwidth of 1.565 GHz (-6 dB BW) in addition to the band between 16.50 and 17.80 GHz for 5G. The design is planar, low profile, simple, and compact in structure making suitable for wireless handheld devices and mobile terminals. The measured gain at 3.46 GHz was at least 2.22 dBi and at 17 GHz was 8 dBi for the 4G and 5G MIMO antenna systems, respectively. The envelope correlation coefficient was also calculated from the measured 3-D patterns and showed good MIMO performance. This is the first integrated 4G/5G MIMO antenna system with below 6 GHz and above 10-GHz covered bands using CAA.