It depends. The letter of commitment is valid as long as the promisor signs it, and whether the promisee signs it or not does not affect the validity of the letter of commitment. Article 32 of the Contract Law; "If the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign or seal it." Generally speaking, a contract is valid only if it meets the effective conditions stipulated by law, otherwise it may not only be invalid, but also be bound by law.