Internet of Things (IoT) technology has developed rapidly today. IoT is widely utilised as an enabler for several concepts, such as Smart City, Smart Farming, and Smart Systems. In addition, mobile applications have an essential role in the IoT ecosystem, where IoT functions for interaction, monitoring and control can be done quickly. The combination of IoT and mobile applications can be a crucial factor in the operation of a system and can be done remotely. In addition, mobile applications can also utilise the data that has been collected to provide better insights to users. That helps users make wiser and more optimal decisions. However, creating mobile applications, especially for IoT systems, is sometimes limited to monitoring and control, so it becomes a basic application and low feature. However, with good application design or design, it can provide comfort and added value for users. Usability is essential in developing application products, and this should be noticed. This research conducts usability testing using the Maze Design platform on the urban farming IoT application prototype. The results of this research can measure the usability score from the calculation of various essential aspects and provide insights into optimising mobile application design, especially for IoT systems.