The 250-foot-long kiln was found near the city of Jingdezhen, once the center of China's ceramics industry, China's state-run Xinhua news agency reported.
Dragon kilns were long, sloping chambers with a firebox at one end and a flue at the other.
The kiln, said the be the longest ever found from that period, was unearthed in the ruins of Nanyao Village, Xu Changqing, head of Jiangxi cultural relics and archaeological institute, said.
Many tons of tools and ceramic fragments were also found at the ruins, which cover around 1,200 square yards, an institute spokesman said.
First discovered in 1964, the Nanyao ruins were not excavated then as techniques for preserving unearthed relics were very poor at the time.
Recently there has been academic debate as to exactly when Jingdezhen started firing porcelain, leading to the decision to examine the Nanyao ruins, Xinhua said.