Zhao Gao (died c. October 207 BC) was a Chinese politician. He was an official of the Qin dynasty of China. Allegedly a eunuch, he served as a close aide to all three rulers of the Qin dynasty – Qin Shi Huang, Qin Er Shi and Ziying – and was regarded as having played an instrumental role in the downfall of the dynasty.

Zhao Gao started his career under Qin Shi Huang as Prefect of the Office for Imperial Carriages (中車府令), an official in charge of managing the palace's horse-drawn carriages. During this period of time, he also served as an attendant to Huhai, Qin Shi Huang's youngest son, and tutored him in the laws of the Qin Empire. In 210 BC, after Qin Shi Huang died in Shaqiu (沙丘; south of present-day Dapingtai Village, Guangzong County, Hebei), Zhao Gao and Li Si, the Chancellor, secretly changed the emperor's final edict, which originally named Fusu, the crown prince, the heir to the throne. In the falsified edict, Fusu was ordered to commit suicide while Huhai was named the new emperor.

After Huhai was enthroned as Qin Er Shi, he promoted Zhao Gao to Prefect of the Gentlemen of the Palace (郎中令), an official post whose duties included managing the daily activities in the imperial palace. Zhao Gao, who was highly trusted by Qin Er Shi, instigated the emperor to exterminate his own siblings to consolidate power, and used the opportunity to eliminate his political opponents, such as Meng Tian and Meng Yi. He also framed Li Si for treason and had Li Si and his entire family executed, after which he replaced Li Si as Chancellor and monopolised state power.

In 207 BC, when rebellions broke out in the lands east of Hangu Pass, Zhao Gao became worried that Qin Er Shi would blame him, so he launched a coup in Wangyi Palace (望夷宮; in Xianyang, near present-day Xi'an, Shaanxi) and assassinated the emperor. Following Qin Er Shi's death, Zhao Gao installed Ziying, Fusu's son (allegedly; there is no firm consensus on what Ziying's relationship to the Qin royal family really is), on the throne. Ziying sent Han Tan (韓談), a eunuch, to assassinate Zhao Gao.

Zhao Gao was distantly related to the royal family of the Zhao state of the Warring States period. According to the Records of the Grand Historian, Zhao Gao's parents committed crimes and were punished. His brothers were castrated; it is unclear whether Zhao Gao himself was a eunuch or not. However, Qin Shi Huang valued Zhao Gao since he was learned in criminal law.^{[clarification needed]} This was very useful to Qin Shi Huang since he himself was always looking for ways to control the people by laws and punishments. Zhao Gao enjoyed a steady rise in position.

When Zhao was a minor official, he committed a crime punishable by death. Meng Yi was the official in charge of sentencing and he sentenced Zhao to death and removed him from the officials list as instructed by Qin Shi Huang. Zhao was later pardoned by Qin Shi Huang and returned to his official status.

At the end of the reign of Qin Shi Huang, Zhao Gao was involved in the death of Meng Tian and his younger brother, Meng Yi. Meng Tian, a reputable general and a supporter of Qin Shi Huang's eldest son, Fusu, was stationed at the northern border, commanding more than 200,000 troops for the inconclusive campaign against the Xiongnu. Following the sudden death of Qin Shi Huang at Shaqiu, Zhao Gao and Li Si, the Chancellor, persuaded the emperor's youngest son, Huhai, to falsify the emperor's will. The fake decree forced Fusu to commit suicide and stripped Meng Tian of his command. Harbouring hatred for the entire Meng family due to his prior sentencing by Meng Yi, Zhao Gao destroyed the Meng brothers by convincing Huhai to issue a decree that forced Meng Tian to commit suicide and execute Meng Yi.

Qin Er Shi, who viewed Zhao Gao as his tutor, became the next Qin emperor.