Abstract: Mencius’ thoughts are not like those of Confucius who defined the duties of different social roles. They even go beyond that and stress the equality among all the roles. Further, they are characterized with a spirit of contract. From a perspective of theory of social contract, we can treat them as a kind of “inherent contract” which has five features. Firstly, the equality of all subjects is one based on the inherent virtue. Secondly, what the contract attempts to defend is the society which is to realize the inherent virtue instead of external lust for personal interest and fame. Thirdly, the execution of the contract mainly depends on the internal moral consciousness instead of external force. Fourthly, the responsibility to defend the contract mainly falls on the Shi class. Fifthly, the contract is to protect people’s interest instead of maintaining king’s sovereign.