In distance education system, the learning process should be assessed using a self-learning instrument for the reason to measure learning competency. So, it should not be measured by the instructors feeling. In practicing writing III course, students are demanded to practice writing, whereas measuring the writing competency is needed to identify the progress of writing practice. To meet this need, this study attempts to develop a self-assessment instrument through an Instructional System Design Method. To assess the writing III course the instrument was developed through 5 steps: (a) analyzing material of writing III courses by which module writing III was used as area of study, (b) developing the blue print of the manual, (c) deciding the purpose of the manual (d) developing the manual guidance/directory and (e) developing exercises and the answers key. The quality of the writing self-assessment instrument was analyzed by experts and tutors of the writing III course. A thirty (30) students coming from English Language Departement of Teacher Traning Universitas Terbuka registered in 2008. 1 were chosen to write their comments about the instrument. Data was collected using close and open questionaires and was analysed through three (3) stages: reducing , categorizing and defining/interpreting. It was revealed that the quality of the manual self-assessment fulfilled the seven criteria of writing assessment, namely good format, good appearance, simple language, easy to use, usefull, innovative and brief content.