Provable data possession is a technique for ensuring the integrity of data in outsourcing storage service. In this paper, we propose a cooperative provable data possession scheme in hybrid clouds to support scalability of service and data migration, in which we consider the existence of multiple cloud service providers to cooperatively store and maintain the clients' data. Our experiments show that the verification of our scheme requires a small, constant amount of overhead, which minimizes communication complexity. Categories and Subject Descriptors H.3.2 [Information Storage and Retrieval]: Information Storage; E.3 [Data]: Data Encryption General Terms Design, Performance, Security Keywords Storage Security, Provable Data Possession, Hybrid Clouds