Abstract: A guaranteeing server and a guaranteeing method for transaction on blockchain are disclosed. The guaranteeing server is coupled to a blockchain network and comprises a memory unit and one or more processing units. The memory unit stores a plurality of instructions and the processing units execute the instructions to perform steps of: receiving a transaction data from a user, wherein the transaction data includes a wallet data including a wallet address data and a user's signature data; checking whether a cryptocurrency balance associated with the wallet address data on the blockchain network is sufficient to execute the transaction; when the cryptocurrency balance is sufficient to execute the transaction, transmitting the transaction data to the blockchain network for performing a blockchain operation; and transmitting a transaction guarantee information corresponding to the transaction data to an opposing party of the transaction.