To provide hetero-shrinking combined polyester filament yarn that gives fabrics of wool-like fabric hand with reduced fluff and high bulkiness and manifests excellent deep color dyeing.

The sheath yarn is prepared by heat-treating a polyester half-drawn yarn having a boiling water shrinkage of ≤ 5 % under relaxation, the core yarn is a polyester yarn having a boiling water shrinkage of ≥ 8 % and the core yarn and the sheath yarn are entangled with each other to give the hetero-shrinking combined filament yarn. In this case, both polyesters constituting the core yarn and the sheath yarn are produced by the polycondensation reaction in the presence of a catalyst comprising a reaction product between a specific titanium compound and a phosphorus compound.