PURPOSE: To obtain multifilamentary polyester yarns having latent structural difference between constitutent filaments capable of producing remarkable difference in filamentary length, by combining a low oriented polyester filamentary yarns containing a polymer with highly shrinkable polyester filamentary yarns.

CONSTITUTION: (A) A polymeric composition containing (i) polyethylene terephthalate and/or polytetramethylene terephthalate and (ii) a styrene polymer and/or (meth)acrylate polymer in an amount of 0.4W8wt% based on the component (i) and (B) a copolymeric polyester composition are extruded through separate extrusion holes without mutual mixing with one another, and the extruded filaments are cooled, doubled and taken off to give the aimed filamentary yarns constituted of filamentary groups of the component (A) and copolyester filamentary groups of the component (B) having a lower average elongation at break and higher shrinkage in boiling water than those of the filamentary yarn groups of the component (A).