Oak floors are usually light in colour with a yellowish hue. When a dog has an accident on oak floors, the urine can show up as a dark stain. The best way to remove a stain from oak floors is to lighten it to match the wood. Bleach can lighten the stain too much, so a gentler method is necessary.
Put a couple of paper towels over the stain if it is fresh to soak up any urine that you can.
Soak a cotton ball in hydrogen peroxide, and squeeze out the excess liquid.
Dab the stain with the cotton ball. Do not soak the stain with hydrogen peroxide. Too much will bleach the wood too much.
Let the area dry completely, and then repeat the process three times.