There is provided a method for treating papermaking waste water, which comprises having a silica-aluminum based inorganic polymer flocculant having an Si/Al molar ratio of 0.2 to 1.5 contained in papermaking waste water having a pH or adjusted pH of 5 to 14 such that the concentration of the inorganic polymer flocculant becomes 1 to 250 (mg-Al/L) in terms of aluminum to control the pH of the papermaking waste water to 5 to 8 and then adding an organic polymer flocculant. The method for treating papermaking waste water has high suspended material flocculation efficiency and can flocculate suspended materials without leaving fine suspended materials and produce a flocculated precipitate which can be recycled as a valuable resource.