Face-to-face and one-to-one human tutoring is the best tutoring field. Human tutors are not always and everywhere available and that's why computer based tutoring is developed. Intelligent Tutoring System (ITS) is the software system developed for tutoring human subjects, when human tutor is not available. ITS performance is not as good as human tutors, but ITS domain is improving and recently gaining much popularity. An ITS development project can involve an interdisciplinary team of experts from the domains of learning sciences, cognitive sciences, software engineering, and Human-computer interaction (HCI). ITS is a software intended to be used by human user; any software development project involves designing of user interfaces. Although ITS development has improved, but most of the development has focused on learning sciences and mostly ignoring the user interfaces. This has resulted in current ITS with efficient learning modules, but less efficient interface design. Performance of a software can be measured by it usability, and one way to define quality of a software is by its "ease of use". Software that is not easy to use by its user can be considered of lower quality. This paper reviews the literature of ITS and usability; with the intention of indicating the currant gap between ITS development and usability of the system. This article also presents a discussion which can provide future directions in ITS development with usability context.