In a Facebook announcement posted at noon, the embassy said it had received a report from South Korean police that at least one Thai national was killed in the crush.
The embassy said it was coordinating with South Korean police for more information on the Thai casualty so that it could inform the victim’s family as soon as possible.
The embassy said it would assist the family in repatriating the body to Thailand.
Earlier on Sunday, the embassy had said that there were no reports of Thais among the 151 victims of the stampede.
South Korea's fire department told AFP news agency that 19 of the 151 people killed during the incident were foreigners. Yonhap news agency added that nationals from Iran, Uzbekistan, China and Norway were among the dead.
The embassy also advised Thais in Seoul to avoid joining festivities with large crowds in attendance.
Thais in South Korea can contact the embassy for assistance at 010 6747 0095 or 010 3099 2955.