Urine, whether from humans or pets, can stain your wood floors. When the urine stain is old, ammonia in the urine causes discoloration and a lingering odor. The moisture in the wood, from the urine, can also lead to mold or mildew, turning the wood black. While it's best to remove urine stains from your wood floor immediately, older stains can be removed, as well, with a little extra effort.
Pour hydrogen peroxide directly onto the old urine stain on your wood floor. Use enough to wet the wood without producing a puddle. The peroxide may foam, which is normal.
Saturate a clean cloth with the peroxide. Place the cloth on top of the old urine stain on your wood floor. Tear off a piece of plastic wrap large enough to cover the peroxide-soaked cloth and stained area of the floor.
Lay the plastic wrap over the cloth to make a stain-lifting poultice. Let the poultice sit on the old urine stain until the next morning. The poultice will remove the urine stain and kill mold or mildew.
Remove the poultice from the wood floor. Mix equal parts white vinegar and water and dip a clean cloth in the solution. Rinse the floor with the vinegar solution, then dry with another clean cloth. Allow the floor to dry.
Cover the urine-stained area with a liquid pet odor neutralizer. Allow the neutralizer to sit on the wood for a few hours before wiping off with your diluted vinegar solution. Pet odor neutralizer has enzymes that will break down and absorb any odor-causing bacteria the urine stain has left, whether from pet or human urine.
Sand off any remaining discoloration left by the urine stain. Rub the sandpaper against the wood, moving with the wood grain so you don't scratch the wood surface. Use 80- to 100-grit sandpaper so you can sand off the stain without sanding down a substantial amount of the surface.
Sweep up the dust off the floor, using a broom and dustpan, then wipe the floor with a clean cloth dampened with vinegar. Use a matching color of wood finish to touch up the dried area of wood where the stain has been removed by applying the wood stain touch-up with a paintbrush. Follow directions on the wood stain package.