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.
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.
On 4 May, the opening day of the meeting, she claimed a 500 guinea prize without having to race, when her opponent, a filly named Tancreda, was withdrawn from a scheduled match over five furlongs.
[6] A month after her classic win "Mouse" was moved up in distance for the Oaks Stakes over one and a half miles at Epsom Downs Racecourse.
[9] Another success in a 200 guinea match race followed at the Second October meeting when she beat the four-year-old Bobadilla (who had been favoured in the betting) over the Ditch Mile course.
[11] On 31 October, the last day of the Newmarket season Young Mouse was beaten in a ten furlong match by Lucetta, a filly who went on to win the Ascot Gold Cup in 1830.
[13] Young Mouse produced six foals in the United Kingdom, including the versatile colt Rat-trap (who died in 1839) and the future stallion Mus.