If the borrower's signature on the back of the IOU is consistent with the handwriting on the front of the IOU, it has legal effect. Otherwise, the legal effect of the IOU is to be determined, and other evidence needs to be collected to prove the loan relationship.

The legal basis is the Contract Law of People's Republic of China (PRC).

Article 32 A contract is concluded by the parties in the form of a contract, and it is established when both parties sign or seal it.

Chapter III Validity of Contract

Article 44 A legally established contract shall come into force upon its establishment.