Provided is a duplex printer and method of duplex printing. The duplex printer and method of printing includes a paper feeding belt that is vertically installed to form a first vertical surface; a photosensitive drum that is installed to contact the first vertical surface; and a transfer roller that is installed to contact an other surface of the first vertical surface contacting the photosensitive drum to transfer a toner image from the photosensitive drum onto a sheet of paper, which is supplied between the photosensitive drum and the paper feeding belt. A back surface feeding path of the paper is formed at an opposite side of the photosensitive drum in the paper feeding belt, and the paper is conveyed closely adhered to a surface of the paper feeding belt in the back surface feeding path of the paper.