Clear away loose rust particles using a wire brush on the cage. Run the wire brush up and down in the same direction as the bars of the cage. Wipe the rust particles off of the bottom of the cage with a rag when you are finished.
Spray down the cage with hairspray, which will remove rust but is not toxic to most animals or people.
Wait several minutes while the hairspray works into the rust.
Scrub the rust again using the wire brush.
Continue using the hairspray and wire brush to remove layers of rust from the cage.
Rinse the cage with water to remove the hairspray when you're finished, and dry it thoroughly to prevent more rust from forming.