Young Mouse (1826–1843) was a British Thoroughbred racehorse and broodmare who won the sixteenth running of the classic 1000 Guineas at Newmarket Racecourse in 1829. In a racing career which lasted from May 1829 until July 1830 the filly ran six times and won three races. Young Mouse won the 1000 Guineas on her first competitive appearance and then ran unplaced in the Oaks Stakes before winning two match races at Newmarket in autumn. She was retired from racing after a single, unsuccessful run as a four-year-old. Young Mouse was later exported to France where she had some success as a broodmare.