Problem-based learning (PBL) is proposed as one of the most well-known alternatives to subject-based learning in educating graduates to become independent workers, critical thinkers, problem solvers, lifelong learners, and team workers. However, the PBL practice is still far from widespread. One of serious impediments to PBL’s diffusion in education is that teachers have difficulties in transforming a subject-based course into a problem-driven course. In addition, teachers lack the necessary skills to make informed judgments and decisions about how to use technologies in their PBL practices. The purpose of this research is to support teachers in developing an online PBL unit. Based on schema theory we developed a PBL scripting language and an associated PBL authoring tool. The tool was developed for teachers to represent, communicate, and reuse their PBL course/lesson plans implementing in technology-enhanced learning environments. It is assumed that it can also be used as a means to educate teachers who may be not familiar with PBL to learn PBL design and to develop an online PBL unit. Through conducting an experiment we found that the PBL authoring tool can facilitate teachers to make informed decisions in their design practice through following a formal design method. Most participants of the experiment thought that the tool is useful to design an online PBL unit and easy to learn.