To clean a urine-stained mattress, soak up any moisture and apply hydrogen peroxide and baking soda to the stain. The stain can also be removed with an enzyme-based cleaner.
Soak up any excess urine by pressing on the stain with a towel, and then apply a solution of 3 percent peroxide to the stain. Allow the peroxide to remain on the stained area for up to five minutes, and use a clean, dry towel to soak up the peroxide. After removing the peroxide, sprinkle the stain with a liberal amount of baking soda to remove the remaining moisture and to eliminate odors.
Allow the baking soda to remain on the mattress for up to 12 hours before vacuuming the area thoroughly with a soft-bristled vacuum attachment. If possible, allow the mattress to dry outdoors in a sunny location, or set the mattress up against a wall indoors and place a fan in front of the mattress to hasten the drying process.
Enzyme-based cleaners are an alternative to peroxide and baking soda. To use an enzyme-based cleaner, soak up excess urine from the mattress with a towel and apply the cleaner according to the directions on the packaging. Remove the excess cleaner after the specified amount of time with a clean towel, and then allow the mattress to dry. Dried stains can also be cleaned with enzyme-based cleaners by following the instructions on the packaging.