We report the dark blue nonlinear (C)erenkov 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 with an angle of 30°,twelve bright spots as twice of those in a single PPMgOLN are shown at each second-harmonic Cerenkov ring.The experimental results agree with the theoretical ones and present a promising application in the fabrication of three-dimensional (3D) PPMgOLNs.