This research provides an online worksheet that can help improve students’ argumentative skills in learning physics. The media developed is based on Toulmin’s Argumentation Pattern. The resulting product is an online worksheet that is valid and effective for use in physics learning. The development stage used a 4-D model. Validation was carried out by media experts and learning experts using a questionnaire. The validation questionnaire includes four aspects (Concept Accuracy, Clear Meaning, Physical Appearance, and Element Completeness). Besides, the media was also tested in small groups to determine the user’s response to four aspects (Language Clearness, Attractiveness Layout, Content Understandable, and Communication flow). The effectiveness of the media was measured using a pretest-posttest one group design and the gain score. The argumentation skills test was in the form of ten essay questions. The student answer using TAP components. This study’s results indicate that this online worksheet is valid and effective in encouraging the development of students’ argumentative skills. Three essencial characteristics of the worksheet encouraging the skills are using issues related to daily-life, various media types, and providing many activities.