To provide a method for producing a multifilament processed yarn which gives a woven or knitted fabric having new surface touch, suitable dry touch, suitable volume touch and excellent stretchability, when woven or knitted and then dyed.

This method for producing the multifilament processed yarn is characterized by subjecting a false-twisted synthetic multifilament yarn as a feeding yarn to a revolving processing treatment under an over-feeding state, or false-twisting a synthetic multifilament yarn and then subjecting the false-twisted synthetic multifilament yarn to a revolving processing treatment under an over-feeding state, and controlling the cross-sectional deformation degree of each of the single filaments constituting the yarn to ≤1.2, wherein the cross-sectional deformation degree = (modified cross section degree after the rotation processing treatment/modified cross section degree before the rotation processing treatment).