An eccentric core-sheath composite fiber comprising two kinds of polymers that are ingredient A and ingredient B, wherein, in a cross-section of the composite fiber:
the ingredient A is covered entirely by the ingredient B;
a ratio S/D of a minimum thickness S of a thickness of the ingredient B, which covers the ingredient A, to a fiber diameter D is from 0.01 to 0.1; and
a portion where the ingredient B has a thickness up to 1.05 times the minimum thickness S has a peripheral length of at least one-third entire circumferential length of the fiber. [Claim 2]
The eccentric core-sheath composite fiber according to claim 1, having a stretching elongation of from 20 to 70%,
wherein at least one of the two ingredients is a polyester. [Claim 3]
The eccentric core-sheath composite fiber according to claim 1 or 2, having a single-filament fineness of 1.0 dtex or less and a fineness unevenness (U%) of 1.5% or less. [Claim 4]
A mixed-filament yarn comprising two or more kinds of single filaments having different cross-sectional configuration and dispersedly intermingled with each other, wherein:
at least one kind of the single filaments comprises the eccentric core-sheath composite fiber according to claim 1 comprising a combination of two polymers differing in melt viscosity by 50 Pa∙s or more; and
the at least one kind of the single filaments is bundled with the other of the single filaments with the number of tangles being from 1 to 100 /m. [Claim 5]
A mixed-filament yarn comprising two or more kinds of single filaments having different cross-sectional configuration and dispersedly intermingled with each other, wherein:

at least one kind of the single filaments comprises a composite fiber
comprising a combination of two polymers differing in melt viscosity by 50 Pa∙s or more;
and
the at least one kind of the single filaments is bundled with the other of the
single filaments with the number of tangles being from 1 to 100 /m.
[Claim 6]
The mixed-filament yarn according to claim 4 or 5,
wherein the composite fiber has an eccentric core-sheath composite
cross-section and a three-dimensional spiral structure.
[Claim 7]
The mixed-filament yarn according to any one of claims 4 to 6, wherein the other of the single filaments is a single-component fiber
constituted of a single component.
[Claim 8]
The mixed-filament yarn according to any one of claims 4 to 7,
wherein the composite fiber accounts for 30% or more and 80% or less by
weight of the mixed-filament yarn.
[Claim 9]
A fibrous product comprising the mixed-filament yarn according to any one of
claims 4 to 8 as at least a part of the fibrous product.