The present invention provides a method for the treatment of a crystal slurry by centrifugal washing, including a centrifugal separation step in which a slurry obtained by crystallizing a desired substance from a solution containing an organic component is subjected to solid liquid separation. The centrifugal separation step includes carrying out centrifugal separation to form a cake, and then washing the formed cake with an organic solvent so that the residual organic solvent content of the obtained crystals can be reduced to 1% by mass or less.