Roadside units (RSUs) with caching abilities are becoming an important part for the future transportation system, enabling both Internet accesses and local caching services for vehicular users. In this paper, we address the caching problem which involves the coexistence of multiple service providers who intend to cache their own contents into the RSUs by competitions to improve the data disseminations. And we propose a mechanism based on multi-object auctions, which can achieve a sub-optimal outcome. Simulation results also show the effectiveness of our solution. Categories and Subject Descriptors C.2.1 [Computer-Communication Networks]: Network Architecture and Design—wireless communication Keywords Vehicular network, road-side caching, multi-object auction