IoT helps to minimize the cost and risk, helps connecting and installing thousand and millions of heterogeneous system, provides safe and scalability services and provides better services are the pointed advantages of installing IoT devices on smart city. Building, Environmental monitoring, Waste management, smart parking, smart health, navigation system for transportation, smart grid and autonomous driving are the applications of IoT and smart city. Device integration, networking, device management, security, data collecting protocols, analytics and visualizations supports are the requirements needed for IoT platform. While achieving smart cities IoT challenges are networking issues, transport issues, security issues, confidentiality, integrity, authentication, key and trust management, heterogeneity issues, Denial of service, big data management. The challenges solution provided are cloud, fog and edge computing but this is not sufficient solutions.