This paper describes the requirements for building accessible user interface for users with autism spectrum disorders (ASD) and presents the user interface (UI) of Open Book, a reading assistive tool for people with ASD. The requirements are extracted from both existing research on improving reading comprehension for people with ASD, and from the feedback of users and clinical professionals. The findings are applied in practice to create the user interface of Open Book tool. Key screens of the user interface are presented. It is implied that the features of the UI for people with ASD can be successfully applied to improving overall accessibility of any graphical user interface.