A vehicle door assembly including a vehicle door (12, 46) for opening and closing a get-in/out opening of a vehicle body, the vehicle door (12, 46) comprising: a door body of a hollow sectional shape; an exterior member mounted on a lower section of an outer surface of the outer door body and including an extension section extending downward beyond a lower edge of the door body and a seal member (28, 28A) mounted on the extension section and capable of contacting and sealing a frame section (41, 42), defining the get-in/out opening, when the door (12, 46) is closed, wherein the door body has at least one drainage hole for discharging water having entered an interior of the door body, the seal member (28, 28A) includes a slant section located closer to the frame section (41, 42) than the drainage hole when the door (12, 46) is closed, and the slant section is opposed to the drainage hole and slants downward toward the extension section, wherein the drainage hole is located closer to the frame section (41, 42) than the lower edge of the door body when the door (12, 46) is closed, the seal member (28, 28A) includes a drainage sealing section connecting integrally to the slant section, and the drainage sealing section extends from a lower end of the slant section in a direction toward the door body and extends beneath the drainage hole to the lower edge of the door body, wherein the exterior member includes a seal backup portion having a flat upper surface for supporting thereon a reverse surface of the drainage sealing section, characterized in that the seal backup portion includes a wall section extending downward from an end, located remote from the door body, of the seal backup portion, a surface of the wall section opposite from the reverse surface of the extension section being provided as a seal mounting surface, the seal member (28, 28A) includes a seal mounting section shaped to extend along the seal mounting surface, and the seal mounting section is superposed on and mounted on the seal mounting surface. a door body of a hollow sectional shape; an exterior member mounted on a lower section of an outer surface of the outer door body and including an extension section extending downward beyond a lower edge of the door body and a seal member (28, 28A) mounted on the extension section and capable of contacting and sealing a frame section (41, 42), defining the get-in/out opening, when the door (12, 46) is closed, wherein the door body has at least one drainage hole for discharging water having entered an interior of the door body, the seal member (28, 28A) includes a slant section located closer to the frame section (41, 42) than the drainage hole when the door (12, 46) is closed, and the slant section is opposed to the drainage hole and slants downward toward the extension section, wherein the drainage hole is located closer to the frame section (41, 42) than the lower edge of the door body when the door (12, 46) is closed, the seal member (28, 28A) includes a drainage sealing section connecting integrally to the slant section, and the drainage sealing section extends from a lower end of the slant section in a direction toward the door body and extends beneath the drainage hole to the lower edge of the door body, wherein the exterior member includes a seal backup portion having a flat upper surface for supporting thereon a reverse surface of the drainage sealing section, characterized in that the seal backup portion includes a wall section extending downward from an end, located remote from the door body, of the seal backup portion, a surface of the wall section opposite from the reverse surface of the extension section being provided as a seal mounting surface, the seal member (28, 28A) includes a seal mounting section shaped to extend along the seal mounting surface, and the seal mounting section is superposed on and mounted on the seal mounting surface.