Thin-walled composite sub-elements possess excellent properties, including high specific strength, lightweight, internal torque and moment resistance which offer opportunities for applications in mass transit and ground transportation. In the present work, an open section thin-walled thermoplastic composite frame segment (sub-element) of a mass transit bus was designed, analyzed and manufactured to replace a conventional metal-based design. Three cross-section configurations, rectangular, V-shape and rounded C-shape, were considered, and different lamina stacking sequences, (0/90) 6, ±45/(0/90) 2 s , and ±45/(0/90) 3 were compared. Carbon fiber/polyphenylene sulphide (carbon/PPS) was the material choice, and single diaphragm forming (SDF) process was adopted to manufacture the frame segment. In-plane compression testing was conducted on the manufactured carbon/PPS composite frame to validate the finite element analysis results. A successful design concept to manufacture strategy of the open thin-walled carbon/PPS thermoplastic composite frame segment was demonstrated.