The present invention provides a four-line nylon cutter assembly for a mower in which a winding surface of the spool 30 is divided upward/downward into a first winding surface 330 and a second winding surface 350 by a separating plate 34 provided in the center part, the first winding surface 330 has first through-holes 33 facing each other, and the second winding surface 350 has second through-holes 35 facing each other to be perpendicular to the first through-holes 33 at an interval of Δh vertically； first and second bushings 62 and 66 are installed on coupling parts of the upper case 10 and the lower case 50, respectively； a pair of first bushings 62 are installed to face the first through-holes 33 of the spool 30, respectively； a pair of second bushings 66 are installed at left and right sides to face the second through-holes 35 of the spool 30, respectively, and to be perpendicular to the first bushings 62； while the center part of a first nylon cutter N1 having a predetermined length is positioned in the first through-holes 33, the first nylon cutter N1 is wound around the first winding surface 330 many times and then both end parts of the first nylon cutter N1 are exposed to the outside by predetermined lengths through first withdrawing grooves 63 of the first bushings 62 and while the center part of a second nylon cutter N2 having a predetermined length is positioned in the second through-holes 35, the second nylon cutter N2 is wound around the second winding surface 350 many times and then both end parts of the second nylon cutter N2 are exposed to the outside by predetermined lengths through second withdrawing grooves 67 of the second bushings 66.
