This study aims to develop a valid learning strategy based inquiry to build argumentation skills and to know their effectiveness in building argumentation skills. The method used is the Research and Development (R & D) model of Dick and Carey, by identifying needs and determining goals, analyzing strategies, identifying student characteristics, formulating specific learning goals, developing benchmark reference tests, developing learning strategies, selecting learning materials, formative evaluation, and revision of learning. The object of this research is 75 students who come from 3 high schools in Bandar Lampung. The conclusions of this research are derived from argument inquiry strategy which has the components of learning objectives, learning scenarios, learning approaches, and tools and learning resources. These components are combined with right steps and methods, so the learning strategy effectively for building students argumentation skills.