Su Gui (蘇瓌 or 蘇瑰) (639 – December 18, 710), courtesy name Changrong (昌容) or Tingshuo (廷碩), formally Duke Wenzhen of Xu (許文貞公), was an official of the Chinese dynasty Tang Dynasty and Wu Zetian's Zhou Dynasty, serving as a chancellor during the reigns of Emperor Zhongzong, Emperor Shang, and Emperor Ruizong.
Su Gui was born in 639, around the time that Emperor Gaozong became emperor. He was a great-grandson of the Sui Dynasty chancellor Su Wei, and his grandfather Su Kui (蘇夔) and father Su Dan (蘇亶) also served as officials during Sui and its successor Tang Dynasty. Su Gui himself passed the imperial examination when he was young and was made a military officer at Heng Prefecture (恆州, roughly modern Shijiazhuang, Hebei). When his mother died, his mourning was viewed as so deep and genuine that it got the attention of the chancellor Zhang Da'an, who recommended him for promotion, and he was made a member of the staff of Emperor Gaozong's son Li Dan the Prince of Yu. He was respected by his superiors on Li Dan's staff, Wang Dezhen and Liu Yizhi.
During the reign of Emperor Gaozong's wife Wu Zetian – who seized the throne and claimed the title of "emperor" of a new Zhou Dynasty in 690, interrupting Tang—Su Gui successively served as the prefect of Lang Prefecture (朗州, roughly modern Changde, Hunan) and She Prefecture (歙州, roughly modern Huangshan, Anhui). While he was serving as a prefect, the once-powerful secret police official Lai Junchen was demoted and made a military officer under him. Many people warned Su that he needed to pay particular respect to Lai, as he might be recalled and might become powerful again, but Su rebuffed, pointing out that he was Lai's superior and it was inappropriate for him to flatter someone like Lai. After Lai was recalled in 696, he much resented Su's attitude toward him, and made sure that Su would not himself be recalled to the capital. During Wu Zetian's Chang'an era (701–705) (by which time Lai had died), he was eventually made the secretary general of Yang Prefecture (揚州, roughly modern Yangzhou, Jiangsu) – one of the riches prefectures of the realm, and it was said that his predecessors Zhang Qian (張潛) and Yu Bianji (于辯機) both took much wealth from the prefecture when they left the post, but Su was said to have been so clean that when he left Yang Prefecture to become the prefect of Tong Prefecture (同州, roughly modern Weinan, Shaanxi), he had nothing but a soft mattress in his possession. While Su was at Tong Prefecture, there was a major drought, and the soldiers conscripted from Tong Prefecture thus could not properly prepare for military service. Moreover, at that time, Wu Zetian had sent officials to review governmental actions in the 10 circuits making up the realm, and these officials were strict making sure that the people were submitting taxes and reporting for public works service, much to the distress of the people. Su submitted a petition to Wu Zetian suggesting that those suffering from the drought be exempted from service, and that the circuit-touring officials be recalled. Wu Zetian was said to be pleased with Su, but it is not clear whether she approved his proposal.