To provide a method for producing a resin which contains a phosphonic acid residue, and is good in handleability and has high bulk density.

This method comprises producing a solid resin by injecting a liquid mixture of a resin containing a phosphonic acid residue represented by a specific general formula, a divalent phenol residue represented by general formula (2): wherein R' is selected from the group consisting of H, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a halogen atom and a nitro group; and Y is selected from the group consisting of a single bond, O and S, and a carbonate residue in an organic solvent into a solidifying solvent.