Urine stains often leave a dark, even black, stain on wood floors. When caught and cleaned immediately there is minimal damage to your floors, but often with pets you can't always find the accident when it happens. Oxalic acid applied to the stain will often remove it, but it also ruins your floor's finish and you have to re-stain and refinish the area to match the rest of your floor. There is a way to remove urine stains on hardwood floors that works well for most stains and you won't have to refinish the floor.
Wash the stained area with soap and water and let dry before treating the stain.
Apply a small amount of hydrogen peroxide to the stain using a cloth or your fingers, leaving a slight puddle over the stain. Do not pour it onto your wood floor. Hydrogen peroxide will act like a bleach and lighten the wood, so you should do this slowly.
Allow the hydrogen peroxide to penetrate the stain for a few minutes. If the floor is a darker wood, watch to make sure it doesn't lighten the area too much.
Scrape the wax finish away gently using your fingernail, if it is a small area, or very fine steel wool. The hydrogen peroxide will remove the wax on the surface of the floor, and that's all you want to remove.
Repeat the hydrogen peroxide application.
Cover the treated area with clear plastic. You may have to block the area so that the plastic isn't lifted or pushed off the stain.
Allow the hydrogen peroxide to sit on the floor for two to three hours. For darker woods, lift the plastic frequently to check the lightness of the area.
Wipe the area with a damp cloth. If the stain is still noticeable, you may have to repeat the peroxide application.
Refinish the treated area with wax when the stained area is no longer darker than the rest of your floor.