The rapid growth of Financial Technology (FinTech) has increased the volume and sensitivity of digital financial transactions, raising concerns about data breaches, fraud, and loss of trust. Blockchain technology offers decentralization, immutability, and auditability, but naïve deployments expose transaction details and struggle with scalability and regulatory constraints. This work proposes a blockchain-based framework that integrates smart contracts with privacy-preserving cryptographic techniques to provide verifiable data integrity for FinTech transactions while protecting user privacy and supporting compliance. A private Ethereum-based prototype was implemented using Solidity smart contracts, a Node.js/TypeScript back end, and a synthetic financial-transaction dataset. Performance was evaluated in terms of gas consumption, execution time, integrity verification, and security status. Gas usage remained highly stable (≈141,002–141,015 gas units per transaction), while execution time ranged from about 2.7 to 4.2 seconds, with all transactions successfully confirmed. These results indicate that the proposed framework can deliver predictable on-chain resource use and strong integrity guarantees with acceptable latency for transaction verification and audit functions. The study concludes that blockchain, combined with zero-knowledge techniques, can strengthen data integrity and privacy in FinTech, and suggests future work on Layer-2 scaling, interoperability across platforms, and evaluation with real-world transaction traces.