Among the wide range of realms of possible disabilities after stroke, gait related impairment have been of great interest as walking is a fundamental function of one's daily routine and a key component for the overall quality of life. As solutions, a variety of different types of ankle foot orthoses (AFO) have been introduced throughout the literature. However, improvements in portability and concealment of the system remains unsolved in terms of practicality. In this study, an ankle foot orthosis has been designed focusing on minimizing the weight and size of the orthoses. The orthosis is empowered pneumatically using a portable custom microcompressor. The weight and size reduction was realizable by minimizing the weight and size of the driven output cylinder that was installed to the posterior of the ankle. The finalized weight of the developed AFO was approximately 600g that can provide 15 Nm of assistive torque for ankle plantar flexion.