Abstract: A step assembly that is specifically adapted to assist pets in reaching and/or descending from elevated surfaces is provided. The step assembly has two sidewalls having a plurality of openings in which pegs formed on the sides of individual treads and risers are engaged. The pegs are removably insertable into the openings and include protrusions which create an interference fit upon insertion. Because the treads, risers and side walls are joined by interlocking pegs and openings, the step assembly can be flat packed for shipping, and is easily assembled and disassembled for transportation and/or cleaning.