Yes! While it’s best to use right away, our product will work on old odor stains, even urine. Soak the smelly area with Oxyfresh Pet Stain & Odor Eliminator completely ... an amount equal to the amount of urine. That way it can penetrate deep into the carpet. For the smelliest odors, let it sit for an hour. Afterward, cover with a folded towel and a weighted object (the encyclopedia you’re never going to read would be perfect for this). That will help wick the liquid off the carpet – bonus points if you stand on top of the book. For old stains, you may need to repeat the process twice.