Vehicular Ad Hoc Networks (VANETs) can provide safety and non-safety applications to improve the passenger safety and comfort. Grouping vehicles into platoons in VANETs can improve road safety and reduce fuel consumption. It is critical to design an efficient Medium Access Control (MAC) protocol for Platoon-based VANETs. Moreover, because of the space and time dynamics of moving vehicles, network connectivity is an important performance metric to indicate the quality of the network communications and the satisfaction of users. Unfortunately, network connectivity is often ignored in the design of existing MAC protocols for VANETs. In this paper, we study the connectivity characteristics and present a connectivity-aware MAC protocol for platoon-based VANETs. The connectivity probabilities are analyzed for the Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication scenarios in oneway and two-way VANETs, respectively. A multi-priority Markov model is presented to derive the relationship between the connectivity probability and the system throughput. Based on variable traffic status and network connectivity, a multi-channel reservation scheme is adopted to dynamically adjust the length of the Control CHannel (CCH) interval and the Service CHannel (SCH) interval for the improvement of the system throughput. Analysis and simulation results show that the throughput increases with the connectivity probability. However, with further increase of the connectivity probability, the throughput will decrease due to numerous channel contention. © Copyright 2015 IEEE