This paper presents a four-port multiple-input multiple-output (MIMO) magneto-electric dipole antenna array with high gain and high isolation for 5G millimeter-wave communications. Each antenna contains an eight-way power divider, an eight-element magneto-electric dipole antenna array, a metal rectangular ring, and a dielectric slab. The proposed magneto-electric dipole antenna array has high radiation gain. The metal rectangular ring is applied to not only support the dielectric slab but suppress the surface wave propagation and thus the mutual coupling can be reduced. A further increase in the isolation performance can be realized based on the polarization diversity. The simulated and measured impedance bandwidths at 10 dB return losses are 24–31.86 GHz (28.1%) and 24.12–32 GHz (28.1%), respectively. The simulated and measured isolation levels are larger than 25 and 20 dB, respectively. The simulated and measured realized peak gains at 30 GHz are 20.5 and 19.2 dBi, respectively.