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