A support beam for a pet furniture includes a plurality of back plates, first hooks, second hooks and third hooks. Upper end and lower end of the back plate are formed with an insertion slot and a protrusion respectively. One side of the back plate is formed with a plurality of engaging troughs for allowing the first hooks and the third hooks to be disposed therein. The third hook is engaged with the first hook. By this structure, a shelf plate, a cat house and a cat ladder can be mounted onto the back plate by means of the engagement between the second hook and the third hook. Then, the back plate is fixed to a wall. In this way, the support beam for a pet furniture is obtained.
