The integration of cyber-physical systems (CPS) with smart cities has introduced numerous benefits, such as improved efficiency and sustainability. However, this integration has also raised concerns over security and privacy, particularly in terms of cyber-attacks, data breaches, and unauthorized access. Blockchain technology has been more prominent in recent years as a potential response to these problems. In recent years, blockchain technology has matured as a dependable solution to overcome these challenges. This paper explores the role of blockchain technology in enhancing the security and privacy of CPS in smart cities. It provides an overview of smart cities, CPS, and blockchain technology, and discusses the various security and privacy issues that arise when integrating these technologies. The paper then examines the potential of blockchain technology to address these challenges, including its ability to provide a tamper-proof and decentralized ledger, as well as secure and decentralized data sharing. The paper further discusses about the blockchain based CPS and highlights the existing blockchain-based CPS applications in smart cities and analyses their benefits and limitations to provide insights for policymakers, city planners, and researchers on how to design more secure and efficient smart cities.