Fenomeno (Japanese: フェノーメノ, foaled 20 April 2009) is a Japanese Thoroughbred racehorse and sire. After winning one minor race as a two-year-old he emerged as a top-class performer in the following year, taking the Aoba Sho and St Lite Kinen and finishing a close second in both the Tokyo Yushun and the autumn edition of the Tenno Sho. In his third campaign he won the Nikkei Sho and the spring edition of the Tenno Sho before his season was ended by injury. At the end of that year he was rated the best horse in the world over extended distances. He won a second Tenno Sho in 2014 but failed to win again and was retired to stud at the end of 2015.

Fenomeno is a dark brown horse with a white sock on his right hind leg bred in Hokkaido, Japan by the Oiwake Farm. According to the horse's owner, Sunday Racing, the name Fenomeno comes from the Portuguese word for supernatural events and monster. His trainer, Hirofumi Toda, nicknamed him "Mamechin" (Japanese: マメチン), due to the fact that his coat color resembles a type of sweet black soybean served during New Year’s, known as Kuromame (Japanese: 黒豆).

His sire, Stay Gold, a son of the thirteen-time Leading sire in Japan Sunday Silence, was a successful international performer, winning the Dubai Sheema Classic and the Hong Kong Vase. Standing at stud at the Big Red Farm in Hokkaido, he produced numerous important winners including Gold Ship, Orfevre, and Nakayama Festa. Fenomeno's dam, De Laroche, showed some racing ability, winning a maiden race in her native Ireland as a three-year-old and a minor contest in the United States at four. In November 2003 at the Fasig-Tipton Kentucky Fall sale she was bought for $140,000 by Haruya Yoshida and exported to become a broodmare in Japan. She was a half-sister to the Hong Kong champion Indigenous and as a descendant of the British broodmare Felucca (foaled 1941) was related to numerous major winners in Europe including Bireme, Longboat, Cut Above, Bolas and Sharp Edge.

During his track career Fenomeno was trained by Hirofumi Toda and carried the black, red and yellow colours of Sunday Racing.

Fenomeno made his racecourse debut in a contest for previously unraced juveniles over 2000 metres at Tokyo Racecourse on 30 October and came home first ahead of thirteen opponents. He was then moved up in class for the Listed Hopeful Stakes over the same distance at Nakayama Racecourse on 25 December and finished seventh of the sixteen runners behind Admire Blue.

On his three-year-old debut, Fenomeno won a minor race over 2000 metres at Tokyo on 29 January, beating the subsequent Tenno Sho (autumn) winner Spielberg into second place. He then stepped up in class for the Yayoi Sho (a trial for the Satsuki Sho) at Nakayama and finished sixth of the fifteen runners behind Cosmo Ozora. On 28 April the colt was moved up in distance for the Grade 2 Aoba Sho over 2400 metres at Tokyo and started the 1.1/1 favourite against sixteen opponents. Ridden by Masayoshi Ebina, who became his regular jockey, he recorded his first important success as he came home two and a half lengths clear of Etendard. The colt was then moved into the highest class to contest the Tokyo Yushun on 27 May in which he started at odds of 13.6/1. He was less fancied than Sunday Racing's other two runners World Ace (the favourite) and Deep Brillante with the best of the other runners appearing to be Gold Ship and Grandezza (Spring Stakes). Coming from well off the pace, Fenomeno produced a strong, sustained run on the outside, but just failed to overhaul Deep Brillante and was beaten by a nose in a photo finish.

After a break of three and a half months, Fenomeno returned at Nakayama in September for the St Lite Kinen, a race which often serves as a trial race for the Kikuka Sho. He started evens (1/1) favourite in a seventeen-runner field and won by a length from the outsider Sky Dignity after taking the lead early in the straight. He was then matched against older horses in the autumn edition of the Tenno Sho over 2000 metres at Tokyo on 28 October and was made the 2.4/1 favourite. He made steady progress on the outside in the straight but was beaten half a length into second place by the five-year-old Eishin Flash. Fenomeno ended his season with a run in the Japan Cup on 25 November in which he stayed on well to finish fifth of the seventeen runners behind Gentildonna, Orfevre, Rulership and Dark Shadow.

Fenomeno began his third campaign in the Grade 2 Nikkei Sho over 2500 metres at Nakayama on 23 March and started the even money favourite in a fourteen-runner field. After tracking the leaders the colt was switched to the outside in the straight, took the lead inside the last 200 metres and won by one and a half lengths from Capote Star. On 28 April Fenomeno contested Japan's premier extended distance race, the spring edition of the Tenno Sho over 3200 metres at Kyoto Racecourse and started the 5.2/1 second choice in the betting behind the odds-on favourite Gold Ship. The veterans Meiner Kittz and Jaguar Mail, winners of the race in 2009 and 2010 respectively were again in the field while the other fourteen runners included Red Cadeaux and Admire Rakti. After racing in mid-division, Fenomeno moved up to join the leaders on the final turn and took the lead 400 metres from the finish. He accelerated clear of the field and won "readily" by one and a quarter lengths from Tosen Ra with Red Cadeaux three and a quarter lengths back in third. After the race Ebina said "I just wanted to get into a good position during the trip, which I managed to do. He had a good first lap which I thought was key. I wasn’t sure what the pace was like; all I was thinking about was keeping the horse in a good rhythm. I was expecting Gold Ship to come and get us at some point but I wasn’t worrying about it. If he passes us, he passes us. My job was to get the most out of my horse."