The　aim　of　this　study　is　to　present　a　novel　shape-transformable　polyhedral　mechanism　namely,　the　TrT-T　mechanism,　which　can　transform　between　a　truncated　tetrahedron　and　a　common　tetrahedron.　The　conceptual　model　of　the　TrT-T　mechanism　is　proposed　and　described.　For　one-degree-of-freedom　objective,　a　hexagonal　planar　linkage　is　chosen　as　a　hexagonal　interlinked　unit　to　develop　a　solid　model　and　fabricate　a　prototype.　Mobility　analysis　is　carried　out　based　on　screw　theory.　The　inverse　and　forward　kinematics　are　investigated,　and　the　singularity　is　analyzed.　The　trajectories　and　velocities　of　the　hinge　points　are　described　and　explored.　The　prototype　and　simulation　results　demonstrate　the　feasibility　of　the　TrT-T　mechanism　for　shape　transformation　and　validate　the　correctness　of　the　mobility　analysis.　As　a　novel　polyhedral　linkage,　the　TrT-T　mechanism　can　be　potentially　applied　to　modules　with　shape-transformation　ability　for　constructing　reconfigurable　and　modular　robots.