Engineering design ability is critical in today’s society due to the vast development of technology. However, the development of it is not easy. The introduction of STEM (Science-Technology-Engineering-Math) and the utilization of PBL (Project-based Learning) seem to promise a bright future in the development of such ability. We adopted Atman’s Engineering Design Process to evaluate the progress that students made after learning from a project-based Truss Tower STEM course. Students were grouped in six to design and construct a light-weight water tower type truss structure that can withstand severe earthquake. 137 students participated in this course and took pre-test as well as post-test. Students demonstrated significant progress in Developing Alternative Solutions and Project Realization. However, students did not show significant progress in Problem Scoping. Our research result echoes earlier research that some of engineering abilities might be trainable in classroom while other abilities might need other development methods.