The advent of network storage services has revolutionized user experiences worldwide, offering unparalleled convenience, cost-effectiveness, and robust availability. However, relying solely on a single service provider entails inherent risks. To address this, sophisticated multi-cloud storage systems have emerged, aiming to mitigate data corruption risks. Nevertheless, ensuring data integrity in such systems necessitates robust auditing schemes. Traditional approaches often depend on centralized entities like third-party auditors (TPAs) or cloud service organizers, leaving users vulnerable to malicious actors during disputes. In response, we propose a blockchain-based multi-cloud storage auditing framework. By leveraging blockchain technology, we establish an immutable ledger to record interactions among users, service providers, and organizers, serving as indisputable evidence. Smart contracts are employed to detect and resolve service disputes, compelling untrusted organizers to accurately identify malicious providers. Additionally, we utilize blockchain networks and homomorphic verifiable tags to facilitate low-cost batch verification without the need for TPAs. Theoretical analyses and empirical evaluations demonstrate the scheme's efficacy and cost-effectiveness in multi-cloud environments, promising enhanced data integrity and dispute resolution mechanisms. Keywords—Multi-cloud storage, blockchain, data auditing, dispute arbitration