Multimedia wireless sensor networks (MWSN) have outstanding ability of acquiring and processing information. Media access control is a research hotspot in MWSN. Many MAC protocols with different objectives for wireless sensor networks have been proposed by researchers, however, few of them suit for MWSN. This article presented an overview of characteristics and challenges of MAC in MWSN. We firstly overviewed of the research effort; then we compared different protocols; finally we point out some possible directions of future research on MAC layer design.