In recent years, wireless sensor networks (WSN) have received a lot of attention and several cryptographic protocols have been proposed to protect WSN. However, it still opens that how to balance authenticity and transmission. For authenticating the message from a sensor, the message is appended a Message Authentication Code (MAC) authenticating it. These MACs may result in large amount of transmission, which is the most energy-expensive resource. For reducing the amount of the transmission for the MACs, the exclusive- or (XOR) of the MACs is sent instead. In this way, the transmission can be largely reduced but any error occurred in these MACs would make the authentication failed. All the messages and MACs should be retransmitted. In summary, transmitting all MACs supports better authenticity but worse transmission-efficiency, and transmitting an XOR of all MACs supports better transmission-efficiency but worse authenticity. In this paper, we propose a new scheme based on Reed Solomon Codes for balancing authenticity and transmission effectively. ©2010 IEEE.