Today, IEEE 802.11 Wireless LAN (WLAN) has emerged as a prevailing technology for the broadband wireless networking. Along with many emerging applications and services over WLANs, the demands for faster and higher-capacity WLANs have been growing fast. In this paper, we propose a new medium access control (MAC) scheme for the next-generation high-speed WLANs such as IEEE 802.11n. The proposed MAC, called Multi-user polling Controlled Channel Access (MCCA), is composed of two sub-schemes. The first one is multi-user polling in order to achieve higher network utilization. We also introduce a frame aggregation scheme as the another proposed scheme, which performs aggregations at both MAC and physical (PHY) layers, and can achieve even higher throughput gain as a result. From simulations, we confirm that the proposed MCCA scheme enhances the aggregate throughput of non-quality-of-service (non-QoS) traffic by an order of magnitude from 17.4 Mbps to 129.9 Mbps, while the aggregate throughput and QoS requirements continue to be satisfied.