Emperor Duanzong of Song (10 July 1269 – 8 May 1278), personal name Zhao Shi, was the 17th emperor of the Song dynasty in China and the eighth emperor of the Southern Song dynasty. He was the fifth son of Emperor Duzong and an elder brother of his predecessor, Emperor Gong.
Emperor Gong surrendered to the Mongol Empire in 1276 after the fall of the Song capital, Lin'an (present-day Hangzhou). Zhao Shi and his seventh brother, Zhao Bing, managed to escape southward to Fujian Province, where the new Song capital was established. Zhao Shi was enthroned as the new emperor. However, in 1278, the Mongols broke through the Song dynasty's last lines of defence, forcing Zhao Shi to flee again. Accompanied by ministers such as Lu Xiufu, Zhao Shi boarded a ship and fled further south to Guangdong Province. Thereafter, he stayed temporarily in Hong Kong. The historical relic Sung Wong Toi in present-day Hong Kong's Kowloon City commemorates Zhao Shi's escape to Hong Kong.
In March 1278, while fleeing from the Mongols, Zhao Shi fell from a boat and almost drowned. After his rescue, he became ill and died a few months later in Gangzhou (碙州; present-day Lantau Island, Hong Kong). He was succeeded by his seventh brother, Zhao Bing.