For the first time, large-area, vertically oriented few-layered hafnium disulfide (V-HfS2) nanosheets have been grown by chemical vapor deposition. The individual HfS2 nanosheets are well [001] oriented, with highly crystalline quality. Far different from conventional van der Waals epitaxial growth mechanism for two-dimensional transition metal dichalcogenides, a novel dangling-bond-assisted self-seeding growth mechanism is proposed to describe the growth of V-HfS2 nanosheets: difficult migration of HfS2 adatoms on substrate surface results in HfS2 seeds growing perpendicularly to the substrate; V-HfS2 nanosheets inherit the growth direction of HfS2 seeds; V-HfS2 nanosheets further expand in the in-plane direction with time evolution. Moreover, the V-HfS2 nanosheets show strong and broadened photons absorption from near infrared to ultraviolet; the V-HfS2-based photodetector exhibits an ultrafast photoresponse time of 24 ms, and a high photosensitivity ca. 10(3) for 405 nmlaser.