It is the second time to honour has been bestowed on Gentildonna after her achievements in winning the fillies' Triple Crown in 2012 were marked with the lofty title.
Her trainer Sei Ishizaka said: “I’m honored to receive this award and think it’s the result for her activity through the year.
“She was excellent when winning the Dubai Sheema Classic and then she ruled them all in the Arima Kinen.”
Gentildonna has arrived at the Northern Farm in Abira-cho, Hokkaido where she will stand with King Kamehameha in her first season.
“She will be under lots of pressure as a broodmare,” added Ishizaka. “I want her to be fine and happy forever."
Japan Racing Association award winners
Horse of the year Gentildonna (Sei Ishizaka)
Best 2yo colt Danon Platina (Sakae Kunieda)
Best 2yo filly Shonan Adela (Yoshitaka Ninomiya)
Best 3yo colt Isla Bonita (Hironori Kurita)
Best 3yo filly Harp Star (Hiroyoshi Matsuda)
Best 4yo+ horse Just A Way (Naosuke Sugai)
Best 4yo+ mare Gentildonna (Sei Ishizaka)
Best sprinter Snow Dragon (Noboru Takagi)
Best dirt horse Hokko Tarumae (Katsuichi Nishiura)