Legal analysis: This contract is valid. It is ok to buy a second-hand house without signing an agreement, but it will face great risks. For example, selling one room and two rooms will cause a lot of trouble. If this happens, the purchase agreement is still valid, but it can only prove the existence of the transaction, not prove that the buyer has property rights! .

Legal basis: People's Republic of China (PRC) City Real Estate Management Law.

Article 36 When transferring or mortgaging real estate, the parties concerned shall register the ownership in accordance with the provisions of Chapter V of this Law.

Article 62 When a real estate is mortgaged, it shall be registered with the department designated by the local people's government at or above the county level. Where the land use right and house ownership are obtained due to the disposal of mortgaged real estate, the transfer registration shall be handled in accordance with the provisions of this chapter.