Wireless sensor networks have been studied with two typical applications called event-driven and periodic monitoring applications. Although these applications have different core requirements, they have the same low latency requirement for real-world operation. However, the main issue of the protocol in wireless sensor networks has focused on energy efficiency, so there has been a lack of consideration of the latency problem. In this paper, we propose RA-MAC, an energy efficient and low latency MAC protocol using a new channel access mechanism, and the RTS aggregation scheme for wireless sensor networks. RA-MAC can also provide appropriate characteristics required for both event-driven and periodic monitoring applications through the transmission scheduling scheme. Our experimental results show that RA-MAC not only provides similar energy efficiency but also achieves throughput improvement and latency reduction compared with other MAC protocols.