Many secure electronic payment protocols have been proposed, most of which are based on public key cryptograph. These protocols, however, are not suitable for mobile network due to the limitations of mobile environments, such as limited computation capability of mobile devices, limited bandwidth, etc. In this paper, we propose a private and efficient payment protocol for mobile network, which only involves symmetric key algorithm, such as symmetric encryption, hash function and keyed hash function. All these operations can be implemented on mobile devices feasibly. The proposed protocol also achieves completely privacy protection of buyers, which is one of the important requirements in mobile commerce. First, the identity of the buyer is protected from the merchant. Second, the transaction privacy of the buyer, such as what the buyer buys, and whom the buyer buys from, are also protected from any other parties and financial institutions. By giving a security analysis, we show that our protocol satisfies all security requirements in electronic payment.