The rapid growth of the Internet of Things (IoT) has introduced significant challenges related to security, data integrity, and trustworthiness in distributed systems. Traditional IoT security mechanisms often fail to address vulnerabilities caused by centralized architecture, exposing IoT applications exposed to cyberattacks and unauthorized access. This paper proposes Chain of Things (CoT), a blockchain-based framework designed to enhance the security of IoT applications. By leveraging blockchain's decentralized, immutable, and transparent properties, CoT ensures secure communication, reliable data sharing, and tamper-proof logging of IoT transactions. The proposed framework incorporates smart contracts for automated policy enforcement and scalability, addressing IoT's dynamic and heterogeneous environment. CoT implementation and performance analysis demonstrate its effectiveness in mitigating threats such as data breaches and unauthorized manipulation while maintaining operational efficiency. The proposed framework establishes a robust foundation for securing next-generation IoT systems, promoting trust and resilience in diverse application domains.