Meng Yizi (died 481 BCE), with the clan name Ji, was the ninth-generation patriarch of the Mengsun clan in the State of Lu. His personal name was Heji, commonly known as Zhongsun Heji, and his posthumous title was "Yi," hence he is also called Meng Yizi. He was the eldest son of Meng Xizi (a noble of Lu). Meng Xizi once accompanied Duke Zhao of Lu to Chu to congratulate the completion of the Zhanghua Palace, but he failed to fulfill the mission with proper Li (ritual propriety), which left him with a lingering regret. He resolved to study under those who understood Li. Even on his deathbed, he remained preoccupied with this, instructing Meng Yizi and Nangong Jingshu (also known as Nangong Kuo) to study Li under Confucius. Following their father's instructions, Meng Yizi and Nangong Jingshu became disciples of Confucius.
In the 25th year of Duke Zhao of Lu (517 BCE), incited by Hou Zhao Bo, Duke Zhao attacked Ji Ping Zi, who was besieged on a high platform. Meng Yi Zi (a senior official of the State of Lu) supported Ji Ping Zi, killing Hou Zhao Bo west of the South Gate. Duke Zhao was defeated and fled to the border areas of Lu and Qi, including Yun and Qianhou. In the 12th year of Duke Ding of Lu (498 BCE), Confucius, serving as Grand Minister of Justice (Da Sikou) and acting as prime minister, initiated the "Dismantling of the Three Capitals" (Duo San Du). The Three Capitals were Fei Yi (in present-day Fei County, Shandong) of the Ji Sun clan, Hou Yi (in present-day Dongping, Shandong) of the Shu Sun clan, and Cheng Yi (in present-day Ningyang, Shandong) of the Meng Sun clan. The Three Huan (the three powerful noble families) agreed to this to weaken their stewards' power. Hou Yi was dismantled, and the rebellion of Gong Shan Bu Niu, steward of Fei Yi, was suppressed. Influenced by Gong Lian Chu Fu, steward of Cheng Yi, Meng Yi Zi secretly resisted dismantling Cheng Yi. Ji Sun Si and Shu Sun Zhou Qiu then sided with the Meng Sun clan, causing the "Dismantling of the Three Capitals" to fail. Meng Yi Zi asked Confucius about Xiao (Filial Piety). Confucius replied: "Do not be disobedient." Because the three great officials (including the Zhong Sun clan) often used the rites of the Lu ruler (vassal rites) and even presumptuously used the rites of the Son of Heaven, Confucius answered with "Do not violate Li (Propriety)."