Nowadays, the construction of efficient intelligent transportation system (ITS) has become a new trend for metropolitan cities with increasingly large populations. As one of the most significant component of ITS, the vehicular ad hoc networks (VANETs) are capable of building temporary vehicular sensor networks for efficient and dynamic information exchange between vehicles and road side units (RSUs). As a matter of fact, the traditional VANETs have limited computing and storing capabilities, which restrict the rapid development VANETs services provided to the drivers. Hence, with the rapid development of big data facilities, the cloud-assisted VANETs structure is proposed in order to enhance the capabilities of VANETs. In addition, due to the inherent wireless communication characteristics, data transmissions of VANETs suffer from charted and uncharted security risks and attacks. Thus proper security strategies should be adopted to guarantee secure communication and driver privacy. Emphasizing on the above issues, we develop an efficient cloud-assisted certificateless grouping authentication scheme for VANETs. In our design, vehicle anonymity is provided during the entire communication process. Note that most of the current authenticating schemes assume the secure channel between the RSU and vehicles in order for initial key message transmission, which is not necessary in our scheme.