Joint angles reveal useful information for diagnosis and treatment of some diseases. These are collected with camera-based systems in private rooms. However, these systems have disadvantages including expensive equipment, limited movement area and only indoor use. To overcome these issues, a smart garment is presented to collect knee and ankle joint angles of both legs. With this purpose, accelerometers were placed into garment and obtained raw data was converted into joint angles using scalar product formula. Five subjects participated in experiments and performed level walking, sit-to-stand and stand-to-sit processes. A comparison was done between calculated joint angles by designed system and measured joint angles by single-camera. Overall accuracy of designed system is well over 95%.