It has been reported that hydrogen accumulation along grain boundaries (GBs) is an important process in the hydrogen embrittlement (HE) in pure Ni. However, there are no quantitative studies that elucidate the behavior of hydrogen accumulation and its effect on HE. Consequently, the segregating behavior of hydrogen along GBs and its role in intergranular (IG) fracture in pure Ni were examined in the present research, via a combination of thermal desorption analysis, secondary iron mass spectrometry, Auger electron spectroscopy and slow strain rate tensile testing. It was successfully demonstrated that the hydrogen trapped at GBs and the sulfur segregated along GBs contributed to the hydrogen-trapping. In addition, the contribution of trapped hydrogen on the hydrogen-induced ductility loss was quantitatively investigated. The results revealed a decreased reduction in area (RA) with a concomitant increase in trap-site occupancy, implying that the trapped hydrogen controlled the hydrogen-induced IG fracture and ductility loss in pure Ni.