Carbon　nanotube　(CNT)　fiber　made　from　millions　of　carbon　nanotubes　(CNTs)　that　are　highly-aligned　in　the　axial　direction,　is　lightweight　and　has　many　desirable　properties,　such　as　high　strength　and　high　ductility.　CNT　yarn　is　fabricated　by　twisting　several　CNT　fibers　to　obtain　improved　electromechanical　properties.　In　this　paper,　the　mechanical　behavior　and　electrical　response　of　CNT　fiber　and　their　multi-ply　yarns　under　uniaxial　single　and　cyclic　loads　were　investigated　experimentally.　The　results　reveal　that　the　gauge　factor　of　the　CNT　fiber　is　about　1.65.　For　CNT　yarn,　the　sensitivity　of　the　resistance　variation　decreases　slightly　with　the　number　of　fibers　twisted　in　CNT　yarn　increasing,　while　the　stability　of　resistance　variation　improves.　The　cyclic　test　result　shows　that　the　relative　resistance　changes　linearly　with　strain.　In　addition,　preload　treatment　will　improve　the　stability　of　electromechanical　property　for　CNT　yarn　sensors.