In this work, ultraviolet (UV) photodetectors based on ultra‐nanocrystalline diamond (UNCD) and dispersed graphene flakes (GrF) with ZnO nanotubes (ZnTs) heterostructures are investigated. Unique hybrid nanostructure of dispersed GrF into ZnTs on discontinuous UNCD substrates using scalable techniques is presented. It is revealed from microstructural analysis that the addition of GrF into highly uniform ZnTs grown on UNCD substrates results outstanding UV photodetection properties. Thus, the GrF‐ZnTs/UNCD nanostructure reveals superior UV diode performance, with an ultrahigh UV switching ratio of 19 708 at 5 V, which is excellently better than those of ZnO nanostructures. It is perceived that the perfect distribution of GrF into ZnTs on UNCD substrates results in ultrafast electron–hole recombination. The distribution of GrF and UNCD interlayer enables the new energy levels on the conduction band, which reduces the barrier height to allow fast charge carrier transportation during the UV illumination. It is believed that the addition of GrFs and UNCD layer increase the UV adsorptivity and sufficient amount of conducting path within ZnTs. Therefore, the present GrF‐ZnTs/UNCD photodetector can be used as an efficient UV photodetection device with high performance and opening up new opportunities for future optoelectronic devices.