The farm in Icheon, about 50 miles east of Seoul, was sealed off Tuesday after 110 ducks died there in three days, Yonhap News Agency reported. But researchers say no trace of the H5N1 virus was discovered in the birds.
The quarantine has been lifted, officials said.
More than 6 million birds were killed to prevent the spread of the disease in late 2010 and early 2011 because of an outbreak of H5N1. There have been three earlier outbreaks of the virus in South Korea, the earliest in the winter of 2003-2004.
While transmission to humans is unusual, the mortality rate for known cases of infection is high.