A polyethylene resin composition for use in manufacturing pipe, which has a melt index under a load of 5 kg, at 190 °C of 0.16 g/10 min to 0.24 g/10 min, obtainable by polymerization performed using a Ziegler-Natta catalyst and a 1-hexene co-monomer in a two stage reactor to obtain a polyethylene resin, adding peroxide to the polyethylene resin, and extruding the polyethylene resin mixture by a twin screw extruder to obtain a polyethylene resin composition wherein the extrusion is performed at a temperature of 230 °C to 250 °C and a rate of 1,050 rpm to 1,150 rpm wherein the melt index under a load of 5 kg, at 190 °C, measured according with ASTM D1238 of the polyethylene resin after passing a two stage reactor is 0.32 g/10 min to 0.44 g/10 min; wherein the melt index under a load of 5 kg, at 190 °C, measured according with ASTM D1238 of the polyethylene resin composition after adding the peroxide and passing through the extruder is 0.16 g/10 min to 0.24 g/10 min; and wherein the polyethylene resin mixture comprises; 100 parts by weight of the polyethylene resin, peroxide in amount of 0.001 parts by weight to 0.003 parts by weight with respect to 100 parts by weight of the polyethylene resin, an antioxidant in amount of 0.2 parts by weight to 0.4 parts by weight with respect to 100 parts by weight of the polyethylene resin; and a neutralizing agent in amount of 0.1 parts by weight to 0.2 parts by weight with respect to 100 parts by weight of the polyethylene resin, and wherein the polyethylene resin composition has Zero shear viscosity of 8,000,000 to 12,000,000 poise, determined by using an advanced rheometer expansion system (ARES, 190 °C), storage modulus G' and loss modulus G" according to shear rate (unit rad/sec) and calculated through Carreau model, and wherein the polyethylene resin composition has a strain hardening modulus of 53 MPa to 80 MPa measured in accordance with ISO 18488. obtainable by polymerization performed using a Ziegler-Natta catalyst and a 1-hexene co-monomer in a two stage reactor to obtain a polyethylene resin, adding peroxide to the polyethylene resin, and extruding the polyethylene resin mixture by a twin screw extruder to obtain a polyethylene resin composition wherein the extrusion is performed at a temperature of 230 °C to 250 °C and a rate of 1,050 rpm to 1,150 rpm wherein the melt index under a load of 5 kg, at 190 °C, measured according with ASTM D1238 of the polyethylene resin after passing a two stage reactor is 0.32 g/10 min to 0.44 g/10 min; wherein the melt index under a load of 5 kg, at 190 °C, measured according with ASTM D1238 of the polyethylene resin composition after adding the peroxide and passing through the extruder is 0.16 g/10 min to 0.24 g/10 min; and wherein the polyethylene resin mixture comprises; 100 parts by weight of the polyethylene resin, peroxide in amount of 0.001 parts by weight to 0.003 parts by weight with respect to 100 parts by weight of the polyethylene resin, an antioxidant in amount of 0.2 parts by weight to 0.4 parts by weight with respect to 100 parts by weight of the polyethylene resin; and a neutralizing agent in amount of 0.1 parts by weight to 0.2 parts by weight with respect to 100 parts by weight of the polyethylene resin, and wherein the polyethylene resin composition has Zero shear viscosity of 8,000,000 to 12,000,000 poise, determined by using an advanced rheometer expansion system (ARES, 190 °C), storage modulus G' and loss modulus G" according to shear rate (unit rad/sec) and calculated through Carreau model, and wherein the polyethylene resin composition has a strain hardening modulus of 53 MPa to 80 MPa measured in accordance with ISO 18488. 100 parts by weight of the polyethylene resin, peroxide in amount of 0.001 parts by weight to 0.003 parts by weight with respect to 100 parts by weight of the polyethylene resin, an antioxidant in amount of 0.2 parts by weight to 0.4 parts by weight with respect to 100 parts by weight of the polyethylene resin; and a neutralizing agent in amount of 0.1 parts by weight to 0.2 parts by weight with respect to 100 parts by weight of the polyethylene resin, and wherein the polyethylene resin composition has Zero shear viscosity of 8,000,000 to 12,000,000 poise, determined by using an advanced rheometer expansion system (ARES, 190 °C), storage modulus G' and loss modulus G" according to shear rate (unit rad/sec) and calculated through Carreau model, and wherein the polyethylene resin composition has a strain hardening modulus of 53 MPa to 80 MPa measured in accordance with ISO 18488.