Du Ruhui (585 – 6 May 630[1]), courtesy name Keming, posthumously known as Duke Cheng of Lai, was a Chinese official who served as a chancellor under Emperor Taizong in the early Tang dynasty.

Du Ruhui served on the staff of Emperor Gaozu's son Li Shimin the Prince of Qin, a major general.

Du was scheduled to become the secretary general for Shan Prefecture (陝州, roughly modern Sanmenxia, Henan), when Li Shimin's trusted advisor Fang Xuanling pointed out that Du was highly talented and that Li Shimin could not afford to lose him.

Du later followed Li Shimin in campaigns against Tang's major enemies Xue Rengao the Emperor of Qin, Liu Wuzhou the Dingyang Khan, Wang Shichong the Emperor of Zheng, and Dou Jiande the Prince of Xia, contributing strategies to Li Shimin's campaigns.

Du and Fang continued to serve as key advisors for Li Shimin, and it was said that Fang was capable of planning and strategizing, but was not resolute, while Du was capable of making quick and correct decisions, and they divided their strategical responsibilities while on Li Shimin's staff in that manner.

Fang and Du, initially fearing Emperor Gaozu's orders forbidding them to serve Li Shimin, declined.

In anger, Li Shimin sent the general Yuchi Gong to summon Fang and Du, with directions that if they declined again, to kill them.

Li Shimin subsequently ambushed his brothers at Xuanwu Gate and killed them, and then effectively forced Emperor Gaozu to create him crown prince.

Late in 626, when Emperor Taizong personally ranked the contributions of the generals and officials in order to grant them fiefs, Emperor Taizong ranked five of them—Fang Xuanling, Zhangsun Wuji, Du, Yuchi Gong, and Hou Junji to be contributors of the highest grade, and Du was created the Duke of Cai.

In 629, Du, along with Fang, became Puye (僕射), a head of the important executive bureau of the government (尚書省, Shangshu Sheng) and a post considered one for a chancellor.