Legal analysis: In order to have legal effect, an IOU should at least have the following contents: 1, and the title should be IOU. 2. The legal full names of the borrower and the lender should be clearly written (the natural person should write the ID number clearly); 3, should write clearly the amount owed, including the amount expressed in words and figures; 4. The arrears period should be clearly written, including the start and end dates of arrears and a clear arrears period; 5. The specific repayment date should be clearly written; 6. The interest on arrears should be clearly written, with a clear annual interest rate or monthly interest rate. Finally, the total amount of interest on arrears (including the amount in words and figures) should be paid: 7. The date, month, day, time and payment method of repayment of principal and interest in arrears should be clearly written; 8, how to deal with overdue, mainly how to calculate interest, whether there is a penalty; 9. There should be the debtor's autograph, handprint or autograph (to be printed).

Legal basis: Civil Code of People's Republic of China (PRC).

Article 667 A loan contract is a contract in which the borrower borrows money from the lender, repays the loan at maturity and pays interest.

Article 668 A loan contract shall be in written form, unless otherwise agreed between natural persons.

The contents of a loan contract generally include terms such as loan type, currency, purpose, amount, interest rate, term and repayment method.

Article 669 When concluding a loan contract, the borrower shall, at the request of the lender, provide the true information about the business activities and financial status related to the loan.