A vehicle door assembly is constructed with improved rigidity, which ensures sufficient rigidity even without the formation of pillars in a vehicle. The door assembly includes a front door and a rear door, which each include an outer panel and an inner panel coupled to the outer panel. The door assembly further includes an outer member having upper and lower ends coupled to upper and lower ends of the outer panel, respectively, and spaced apart from the outer panel between the upper and lower ends. The door assembly also includes an inner member having upper and lower ends coupled to upper and lower ends of the inner panel, respectively, and spaced apart from the inner panel between the upper and lower ends. The outer member and the inner member are coupled to each other along the height direction of the vehicle. This forms a closed cross-section between the outer member and the inner member.