The site, located near Fujiacun village in Fengcheng city in Jiangxi province, covers about 18,000 square metres and is surrounded by a moat, Xinhua news agency reported.
About 30 metres of the wall surrounding the ancient city was still standing on its west and pieces of broken tiles were found scattered on the ground, it said.
Villagers said they had seen stone implements at the site in the past, but none was found during a field trip by archaeologists. The researchers said the implements might have been collected by some private collector.
The archaeologists believe the ruins would provide new clues for research on the city structure of the Eastern Han Dynasty, which ruled the eastern part of the country during 24-220 AD.