PROBLEM TO BE SOLVED: To provide a plastic lid for a breeding cage, the lid that has both of air permeability and strength.SOLUTION: A lid for a breeding cage of the present invention is a plastic disposable lid with an opened upper surface for breeding a small animal and fitted in the top edge of the breeding cage. The lid comprises: a flat part an outer frame part positioned in an outer circumference of the flat part, including protrusions on the top from the flat part and grooves below, and fitted in the top edge of the breeding cage a reinforcing part positioned inside the outer frame part, rising in a convex on the top from the flat part, and including a space below and a ventilation part continuously arranged in the reinforcing part, rising from the outer frame part, and forming a gap between the upper part edge of the breeding cage and itself. An air passage is formed for bringing the space of the reinforcing part into communication with the gap of the ventilation part, and connecting between the breeding cage and the outside.
