Abstract: A fishing line comprising a core line and a tubular outer line formed of synthetic fibers and sheathing the core line, the core line being withdrawable from the outer line. A conventional fishing line can be firmly connected to a leader with the outer line by withdrawing the core line from the outer line, then inserting one end of the fishing line and one of the leader into opposite ends of the outer line and tying each of the laps of the outer line over the fishing line and the leader into a single knot. The tied portions are as high as at least 90% in tensile strength ratio.