Abstract: “Nanzhang” was one of Qing Dynasty’s tributary states. It is widely assumed that “Nanzhang” was another name of Laos. The Da Qing Huidian and many other historical sources support this view. However, Laos, which had been a united kingdom in the Ming Dynasty, divided into three parts in the late seventeenth century and early eighteenth century. The northern territory of Laos became a new kingdom, Luang Prabang, which was known as “Nanzhang” in Chinese records. Thus, the view that “Nanzhang” was another name of Laos is mistaken. The provenance and general acceptance of this view is related to some features of information gathering under the tributary system. In the late Qing, people had a better understanding of “Nanzhang”. In fact, many people knew that Siam had annexed “Nanzhang”. Despite this, most people still held the erroneous view that “Nanzhang” was another name for Laos.