Legal analysis
The supplementary agreement may not take effect if it is not stamped. If it is a natural person, the supplementary agreement is still valid without signature and seal; But if it belongs to the company, it needs to be stamped with the official seal, or according to the contents of the contract, the signature of the legal representative is also valid. If it is a supplementary agreement signed between natural persons, the supplementary agreement signed by both parties without seal is valid; If it is a supplementary agreement signed between companies, it generally needs to be stamped with the official seal to be effective. However, if the agreement is valid with the signature of the legal representative, it is also valid without the seal and the signature of the legal representative. It depends on how the contract stipulates. Under normal circumstances, the absence of seal does not affect the validity of the contract, and one of the two parties can sign or seal it to be valid. Unless it is expressly agreed in the contract that it will take effect after being sealed and signed by the legal representative, the supplementary agreement needs to be signed and sealed. The contents of the contract do not violate the mandatory provisions of laws and administrative regulations; The parties to a contract are persons with corresponding civil capacity; The conclusion of a contract by the parties is a true expression of will; The form of a contract can be written or oral.
legal ground
People's Republic of China (PRC) Civil Code
Article 510 After the contract came into effect, the parties did not stipulate or clearly stipulated the quality, price or remuneration, place of performance, etc. They can supplement the agreement; If a supplementary agreement cannot be reached, it shall be determined in accordance with the relevant provisions of the contract or trading habits.
Article 490 Where the parties conclude a contract in the form of a contract, the contract is formed when the parties sign, seal or fingerprint it. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.