The present invention provides a yarn comprising a composite yarn composed of a core part comprising a short fiber and a sheath part comprising a synthetic fiber filament yarn, the core part and the sheath part being integrated via fluff of the short fiber getting between or entangled with the long fibers, the specific gravity of the yarn being adjustable in the range of 1.0 or more, a fishing line comprising the yarn, and a method for producing the fishing line. The present invention provides an ideal fishing line which has a strong core-sheath structure, does not allow separation or detachment of the core part and the sheath part, is easy to handle, and also is excellent in strength, weatherability, and water resistance.