Heterostructures based on two-dimensional (2D) transition metal dichalcogenides semiconductors are reported to be promising building-blocks for next-generation integrated optoelectronic systems, owing to their atomic thin interface and interface-induced properties. Previously reported works have mostly been directed to focus on the 2D/2D heterostructures, and their optoelectronic performance is still inferior to the expectations for practical applications, mainly attributed to their non-ideal optical absorption when the thickness is confined at atomic scale. In this work, we have reported on high sensitivity photodetectors based on one-dimensional (1D)/2D heterostructures consisting of CdS nanowire and WS2 nanosheets grown by direct chemical vapor deposition. The components of the heterostructures were confirmed by x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscope, photoluminescence and Raman spectra measurements, confirming the high quality heterostructures. Photodetectors were then fabricated based on the as-synthesized CdS/WS2 heterostructures, showing superior photodetection performances with a photoresponsivity of ∼50 A W-1 and an ultrahigh photodetectivity of ∼1012 Jones. Much higher responsivity of 5472 A W-1 and detectivity of 5 × 1013 Jones can be achieved through applying back gate voltage. The direct growth of such 1D/2D heterostructures may pave the way toward high performance integrated optoelectronics and systems.