Nowadays, the virtual reality (VR) market has made significant strides. VR is widely used in different applications, and education and training are one of the leading areas which are expected to grow to US $2.2 billion in revenue by 2023. Mixed reality (MR) is also known as hybrid reality that encompasses both VR and augmented reality. It allows interaction and feedback from the users, which is particularly important to enhance the experience in teaching and learning. MR not only merges the real and virtual worlds into a new environment, which combines physical and digital content, but also allows users to interact with the digital content dynamically in real time. In support of teaching and training, MR technology has been applied in diverse manufacturing and industrial sectors to visualize the digital models. Nevertheless, most of these MR projects are mainly focused on users' experience. The effectiveness in comprehending product design is seldom investigated. Therefore, in this project, an MR application is developed for teaching product design to university students. The application is developed on the HoloLens system. A practicable application has been designed that allows students to visualize the geometry of 3-D objects as well as the exploded diagrams of selected components. The students can command the system through the command manual or can signal the system through gazing, gesturing, and voice to implement instructions. To investigate the effectiveness of the MR application in teaching product design, a pretest and a posttest of similar difficulties were designed to access students' abilities in five main areas: the ability of students in comprehending design, understanding product functions, visualizing 3-D geometry, understanding geometric relationship, and students' creativity. In the investigation, 45 students were participated in the tests. Experimental results show that the proposed design positively improves students' understanding in geometric relationships and creativity. In the future, more features will be added to the MR application to further improve students' abilities in learning and training in other aspects.