The purpose of this study was to evaluate the usability of "My AAC", the smart device-based AAC application developed for the communicational disabled. It deals with the usability problem of domestic AAC application in terms of UI to suggest the directionality of development. There were 14 special education teachers who participated in the test. After setting 3 months of field application period, the study analyzed the usability through heuristic evaluation and derives user requirements. Results are followed: first, usability test result was average 3.93 which was above average. Second, among categories, 'match between system and the real world' has the highest score, followed by 'recognition rather than recall', 'availability', 'visibility of AAC application', 'flexibility of system', 'aesthetic and minimalist design', and 'consistency and standards'. However 'error prevention' has the lowest score. Third, the study suggested several issues revealed in usability test. In discussion, considerations on utilizing AAC application as a tool for teaching communication are proposed based on the results.