Emperor Duānzōng (端宗) (1268 – May 8, 1278) was the eighth and penultimate emperor of the Southern Song Dynasty of China who reigned from 1276 to 1278 and died at the early age of ten. He was also known as the "Nation Establishing Duke " (建国公).

Born Zhào Shì (赵昰), his father was sixth Southern Song Emperor Duzong. He became King Ji (吉王) in 1274 and King Yi (益王) in 1276. Enthroned as emperor at Fuzhou on June 14, 1276, his only era took the name of Jǐngyán (景炎 literally: bright flame). Duanzong's temple name means "Final Ancestor".

Duanzong's younger brother Emperor Gong of Song had been captured after the Mongol invasion of Lin'an (present day Hangzhou) in 1276. Duanzong, along with one of his younger brothers Zhào Bǐng (赵昺, escaped to Fujian and established the seat of the government in Fuzhou. In 1278, the Mongol forces were about to breakthrough Song's last line of defense forcing Duanzong to flee. Accompanied by ministers such as Lu Xiufu, Duanzong boarded a ship and fled to the province of Guangdong. Thereafter he stayed temporarily in Hong Kong where the Sung Wong Toi (literally: Terrace of the Sung kings) in Kowloon City commemorates this event.

In March 1278, whilst fleeing from the Mongols, Duanzong fell from a boat and almost drowned. After his rescue, he became ill and died a few months later in Gangzhou (modern day Lantau Island, Hong Kong).

He was succeeded by his younger brother, Emperor Huaizong of Song.