To establish a method for efficiently and economically recovering high-purity useful component(s) from dyed polyester textile products.

The method for recovering useful component(s) from dyed polyester (PES) fiber comprises a dye extraction step, a solid/liquid separation step, a depolymerization step, a transesterification step and a useful component recovering step. Specifically, the method comprises the following process: The dye extraction step is conducted at a temperature higher than the glass transition temperature of the PES but at 220°C or lower using an extractive solvent consisting of a xylene and an alkylene glycol. In the solid/liquid separation step, the dye-extracted PES fiber and the resultant dye-containing extractive solvent are separated from each other. In the depolymerization step, the dye-extracted PES fiber is depolymerized while additionally charging part of a depolymerization reaction liquid to the system to obtain a depolymerization solution. In the transesterification step, methanol is added to the depolymerization solution to conduct a transesterification. In the useful component recovering step, dimethyl terephthalate and the alkylene glycol are separated and recovered from the resulting transesterification product mixture.

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