Metal-organic frameworks (MOFs) based oxygen-evolution reaction (OER) catalyst is an emerging class of highly porous materials that have become increasingly attractive to develop a highly active and stable OER catalyst for overall water splitting. However, it suffers from poor conductivity and inadequate active sites. Herein, we have developed a series of hierarchical Fe-mediated Ni-based metal-organic frameworks (FexNi1-x-MOF) by an adjustable hydrolysis strategy, where the Ni-MOF is used as a template that is decorated with NiOOH active sites. Although Ni-MOF is dissociated during the ion exchange process, the structural integrity is kept for FexNi1-x-MOF as confirmed by the electron micrographs. Moreover, the optimized Fe0.38Ni0.62-MOF catalyst not only exhibits a remarkable OER catalytic performance with a low overpotential of 190 mV at 10 mA cm-2 but also shows a small Tafel slope of 58.3 mV dec-1 and stability. The excellent OER electrocatalytic activity can be attributed to the unique 3D flower-like structure decorated with NiOOH active sites induced by Fe3+ species. This novel methodology expands a new way for the construction of highly efficient alkaline catalytic materials.