The present invention provides a four-line nylon cutter assembly for a mower, characterized in that a winding surface of a 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) formed therein so as to face each other； the second winding surface (350) has second through-holes (35) formed therein so as to face each other and to be perpendicular to the first through-holes (33) at an interval of Δh vertically； first and second bushings (62, 66) are installed on coupling parts of an upper case (10) and a lower case (50), respectively； a pair of left and right first bushings (62) are installed to face the first through-holes (33) of the spool (30), respectively； a pair of left and right second bushings (66) are installed to face the second through-holes (35) of the spool (30), respectively, and to be perpendicular to the first bushings (62)； the center part of a first nylon cutter (N1) having a predetermined length is positioned in the first through-holes (33), and the same is wound around the first winding surface (330) a plurality of times； 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)； the center part of a second nylon cutter (N2) having a predetermined length is positioned in the second through-holes (35), and the same is wound around the second winding surface (350) a plurality of times； and 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).
