This letter presents a wideband decoupling method to suppress the mutual coupling among dual-polarized millimeter-wave antenna arrays for massive multiple-input-multiple-output systems. With the contribution of the proposed decoupling structure, the coupling between elements can be reduced by confining the electromagnetic field propagating along the array aperture plane. An 8 × 8 millimeter-wave dual-polarized antenna array loading with the proposed decoupling structure is further developed. The full-wave simulated results show that an isolation level of over 25 dB can be achieved from 24.3 to 29.7 GHz. The measured results are well in line with the simulated results, denoting that the proposed scheme is effective and valuable for millimeter-wave large-scale antenna array applications.