Marquess Su of Zhao (趙肅侯) (died 326 BCE, reigned 349 BCE – 326 BCE) reigned in the State of Zhao during the early Warring States period of Chinese history.

Marquess Su of Zhao reigned during a time when the authority of the Zhou kings was fast declining. In 344 BCE, the Marquesses of Wei and Qi agreed to recognize each other as kings (thus putting them on parity with Zhou royalty). Angered by the exclusion of his state, Marquess Su laid siege to Wei fortresses in the north. This failed; and in anticipation of possible retaliatory attacks, he ordered the construction of walls along the northern and southern borders, as well as along the course of the Zhang River.

Marquess Su died in 326 BCE. The states of Qin, Chu, Yan, Qi, and Wei each sent ten thousand crack troops to Zhao to attend the funeral. His son, Zhao Yong, succeeded him and became King Wuling of Zhao.

趙肅侯元年（前349年）趙肅侯奪取晉靖公的食邑端氏，將靖公流放到韓國的屯留，靖公被韓國所殺，晉國絕祀。

趙肅侯十七年（前333年）對魏、齊兩國聯合互尊為王一事不滿，包圍魏北部（河南內黃西），不克，被迫撤軍。在南、北邊境、漳水和滏水之間築起長城。在位二十四年卒，秦、楚、燕、齊、魏五國務派銳師一萬人，參加葬禮。子趙雍即位，是為武靈王。