天皇賞
Despite his lack of form in 1998, Grass Wonder was one of sixteen horses selected to run in the Arima Kinen over 2500 metres at Nakayama on 27 December. His opponents included Air Groove (Yushun Himba, Tenno Sho (autumn)), Machikane Fukukitaru (Kikuka Sho), Mejiro Bright (Tenno Sho (spring)), Mejiro Dober (Shuka Sho, Queen Elizabeth II Commemorative Cup), Offside Trap (Tenno Sho (autumn)), Seiun Sky (Satsuki Sho, Kikuka Sho), Silk Justice (Defending Champion), Stay Gold and Yusei Top Run. Grass Wonder won by half a length from Mejiro Bright with a gap of two and a half lengths back to Stay Gold who took third place ahead of Seiun Sky.