The structures of fresh and aged Ni–W catalysts supported on Al2O3 have been analyzed by the XAFS techniques. The local structures around Ni and W in the fresh catalyst were found to be basically the same as those around Ni and Mo, respectively, in Ni–Mo catalysts. For aged catalysts, apparent increases in the coordination numbers of S and W around W were observed relative to the fresh catalyst. The local structure around Ni dramatically changed after aging for 950 h. These results suggest that WS2 slabs grow in the lateral direction during the reaction and that Ni atoms are released from the edge sites of the WS2 slabs.