A door lock with a reinforced fireproof effect includes a lock body mounted on a door and inner and outer operating units mounted to two sides of the door, respectively. The lock body includes inner and outer chassis made of ferrous material or stainless steel having a melting point higher than 1300° C. Inner and outer fixing members coupled with the inner and outer chassis are also made of ferrous material or stainless steel. Thus, these components of the door lock are less likely to melt during a fire, reducing the spreading speed of the fire.