This research is aimed at developing Web-Based Instructional Media in the Indonesian senior high school writing class. The Dick and Carey Model (2009) was employed as the development model. The steps began with identifying instructional goals, conducting instructional analysis, analyzing learners and contexs, writing the performance objectives, developing assessment instruments and instructional strategies, developing and selecting instructional materials, designing and conducting formative evaluation of instruction, revising, and finally designing and conducting summative evaluation. The overall results identified that the Educational Technology Expert validation reached 94.62%, the Media Expert reached 99.04%, and the Matter Expert reached 85.00%. These results proved that the use of Web-Based Instructional Media significantly improved the students’ writing skills. The small group trial demonstrated 78.38%, while the field trial 82.79%; these showed that the Web-Based Instructional Media could be implemented both in the small group and the field trial. In conclusion, the results of the expert validation and the field trials stated that the web-based instructional media is highly appropriate use in improving Bahasa Indonesian students writing skills.