Vehicle ad-hoc networks have developed rapidly these years,whose security and privacy issues are always concerned widely.In spite of a remarkable research on their security solutions,but in which there still lacks considerations on how to secure vehicleto-vehicle communications,particularly when infrastructure is unavailable.In this paper,we propose a lightweight certificateless and oneround key agreement scheme without pairing,and further prove the security of the proposed scheme in the random oracle model.The proposed scheme is expected to not only resist known attacks with less computation cost,but also as an efficient way to relieve the workload of vehicle-to-vehicle authentication,especially in no available infrastructure circumstance.A comprehensive evaluation,including security analysis,efficiency analysis and simulation evaluation,is presented to confirm the security and feasibility of the proposed scheme. Whose ad hoc networks have developed rapidly these years, whose security and privacy issues are always always large. In spite of a remarkable research on their security solutions, but in which there are still lacks considerations on how to secure vehicleto-vehicle communications, particularly when infrastructure is unavailable.In this paper, we propose a lightweight certificateless and oneround key agreement scheme without pairing, and further prove the security of the proposed scheme in the random oracle model. proposed scheme is expected to not only resist known attacks with less computation cost, but also as an efficient way to relieve the workload of vehicle-to-vehicle authentication, especially in available infrastructure circumstance. A security analysis, efficiency analysis and simulation evaluation, is presented to confirm the security and feasibility of the proposed scheme.