A manhole cover maintains a strength and weight the same as those of conventional manhole covers made of cast iron, eliminates the risk of theft, and achieves improved corrosion resistance and sealing properties. The manhole cover comprises: a base unit made of composite materials having compositions containing 12 to 18 wt % of glass fiber, 17 to 23 wt % of a polyester resin, with the remainder being calcium carbonate (CaCO3), wherein the base unit is mounted on the manhole such that an upper portion of the base unit is exposed aboveground; and a metal reinforcement unit which is uniformly distributed within the base unit to reinforce the base unit and increase weight and strength of the base unit.