An adjustable door frame assembly. The door frame assembly is to be adapted to fit door openings of different sizes. The door frame assembly utilizes co-extrusion technic for the components, including PVC foamed plastics frames, a corner connecting metal piece, a U-shape reinforced metal piece and co-extruded soft strips. The corner connecting metal piece fixes two adjacent frames such as the left and the top to form a " " type frame, and then to be joined with the bottom threshold to complete this door frame assembly. The door frame assembly is height or width adjustable by cutting off parts of the side frames to change the dimensions of the door to fit the door openings for different sizes of various buildings.