CNT　fibres　is　composed　of　millions　of　highly　aligned　carbon　nanotubes　along　the　axial　direction,　the　CNT　wires　that　have　more　remarkable　properties　are　twisted　together　by　several　fibres.　In　this　paper,　the　strain-resistance　characteristics　of　CNT　fibre　monofilaments　and　their　multi-ply　wires　are　investigated.　The　experimental　results　show　that　the　gauge　factor　(the　relative　change　in　resistance　per　unit　strain)　of　the　CNT　fibers　is　about　1.50,　which　is　lower　than　the　uniaxial　gauge　factor　of　the　commonly-used　electric　resistances　strain　gauges.　As　the　CNT　fiber　is　elongated,　the　change　of　the　resistance　is　determined　by　the　change　of　both　the　geometric　length　of　the　fiber　and　the　electrical　resistivity.　However,　the　geometric　length　is　the　main　reason.　In　addition,　the　change　of　electrical　resistance　of　CNT　wires　made　of　two-ply　and　three-ply　CNT　fibers　with　uniaxial　strain　are　also　investigated.　The　results　show　that　the　gauge　factor　of　CNT　wires　is　lower　than　that　of　CNT　fibers.　Specifically,　the　change　of　electrical　resistance　of　the　CNT　fibers　and　wires　under　uniaxial　tensile　loading　and　cyclic　loadings　are　analyzed.　The　results　indicate　that　the　change　of　electrical　resistance　of　the　CNT　fibers　and　wires　are　synchronous　with　the　cyclic　strain,　demonstrating　good　stability.　©　2017　International　Committee　on　Composite　Materials.　All　rights　reserved.