We report the dark blue nonlinear Cerenkov radiation by the second harmonic generation （SHG） in a two-layer-stacked hexagonal periodically-poled-MgO： LiNbO3s （PPMgOLNs）. Based on the direct wafer bonding of two target PPMgOLNs rotating around the axis perpendicular to the plane wi twelve bright spots as twice of those in a single PPMgOLN are shown at each second-h ring. The experimental results agree with the theoretical ones and present a promising application in the fabrication of three-dimensional （3D） PPMgOLNs.
