The user interface is the part of the technology used by a person to help them achieve their goals and to isolate their problem. User interface design is part of the design of the user experience, which aims to influence the user's image and experience of using a technological product. In the framework of website and application design, this often means the on-screen graphical user interface, as well as the design of its associated components, so that the use of the site or application is efficient, appropriate and comfortable. To do this, you need to consider the design features of the product, and how to make the user interface more engaging. Interface design has been researched for decades, and has explored features of usability, aesthetics and information processing related to interfaces. The popularity of e-commerce in commerce has increased. Their user interface design must consider not only the above-mentioned features but also the fact that online shops have a transactional aspect. These create certain requirements for the implementation of the user interface. This thesis outlines the basic principles of user interface design. In addition, it explores how these basic principles can be applied in the design of E-commerce user interfaces and how they appear in this context. The thesis aims to answer the research questions: “What is a user interface and its design principles?” And “How do the basic principles of user interface design appear in online shopping?”. The thesis explores the basic principles from three perspectives: general design principles, usability design and visual design. Efforts have also been made to explain the interrelationship between the principles-based solutions in order to achieve a comprehensive understanding. After researching and analysing the literature, the thesis and summary section aims to explain the answers to the research questions, the necessity of the thesis, and possible needs for further research.