The purpose of this study is to design a lesson plan model of project-based learning to teach students in elementary schools. First of all, based on literature review, this author set up four steps to administer project-based learning in schools as follows: a) designing a project, b) planning problem solving, c) solving problems, and d) presenting and assessing products. The first step, designing a project, is to plan a whole project and design specific contents for each step. In the planning problem solving step, students discover real-world problems and plan how to solve the problems. In the solving problems step, students collaboratively work together to solve problems by inquiry and discussion. In the last step, presenting and assessing products, students present their products and students assess them each other. Based on literature review about a lesson plan for applying project-based learning, this author developed a lesson plan model of project-based learning, which can be applied to teach elementary school students. It includes 12 essential elements to engage project-based learning, such as a topic, standards, learning goals, a topic web, a project title, relative subjects, learning order, learning contents, learning activities, learning resources, an assessing plan, and a feedback plan.