A method for processing lithium ion battery scrap includes a leaching step of leaching lithium ion battery scrap and subjecting the resulting leached solution to solid-liquid separation to obtain a first separated solution; an iron removal step of adding an oxidizing agent to the first separated solution and adjusting a pH of the first separated solution in a range of from 3.0 to 4.0, then performing solid-liquid separation and removing iron in the first separated solution to obtain a second separated solution; and an aluminum removal step of neutralizing the second separated solution to a pH range of from 4.0 to 6.0, then performing solid-liquid separation and removing aluminum in the second separated solution to obtain a third separated solution.