Usability is critical to the development of a user-friendly digital textbook platform interface, yet thorough research on interface development based on usability principles is in short supply. This study addresses that need by looking at usability attributes and corresponding design elements from a learning perspective. The researchers used a student survey, log files, and an expert heuristic evaluation to analyze needs for revision in the user interface of the existing Korea Education Research Information Service digital textbook platform. After using suggestions derived from this analysis to develop a new platform prototype, they tested its user interface for usability through a cognitive walkthrough and a formative evaluation. The results show that the usability design elements identified through the use of this iterative design and evaluation model were essential to improving the usability of the user interface and thus facilitating users' actions and learning processes.