A resin composition for producing an insulating material includes (A) 40 to 50% by weight of a base resin formed with a polyolefin-based resin or a derivative thereof, (B) 40 to 50% by weight of a magnesium hydroxide flame retardant of which surface is treated with vinyl silane, (C) 1 to 2% by weight of an antioxidant in which a first antioxidant and a second antioxidant are mixed in a weight ratio of 1:1 to 3, (D) 0.5 to 2% by weight of a lubricant, (E) 2 to 3% by weight of organosilane, (F) 0.05 to 0.2% by weight of an initiator, and (G) 1 to 4% by weight of a catalyst.