A　bistable　composite　tape-spring　(CTS)　is　a　thin-walled　open　slit　tube,　which　can　be　coiled　or　folded　into　two　stable　configurations.　The　CTS　has　been　applied　to　roll-out-solar-array　and　successfully　launched　to　space　station　and　micro-satellites　based　on　their　one-time　deployment　performance.　There　is　growing　interest　on　CTS　to　be　applied　in　reversible　deployable　structures　and　foldable　mechanical　hinges;　however,　its　high-cycle　fatigue　under　large　shape　folding　is　still　unknown.　Here,　we　device　a　novel　folding　fatigue　setup　to　investigate　the　foldingunfolding　cyclic　behaviour　of　the　CTS.　This　is　achieved　by　using　a　bespoke　folding　fatigue　rig,　where　both　the　tape　ends　of　the　CTS　were　clamped　separately　on　rotatable　shafts　to　enable　folding　under　cyclic　axial　displacements.　Since　stress　concentration　is　more　significant　in　the　snapping　fold　region,　analysis　is　focused　on　the　peak　fatigue　stress.　It　is　found　that　the　folding　peak　stress　decreases　with　the　folding　cycle:　although　progressive　local　damage　is　observed　during　3000　to　100,000　cycles,　the　CTS　is　still　functional　and　tends　to　be　stablised　after　300,000　folding　cycles.　The　Basquin＇s　law　is　applied　to　predict　the　fatigue　life　of　the　CTS,　indicating　a　fatigue　life　of　1.4E11　folding　cycles　with　a　40%　decrease　in　peak　folding　stress.　These　findings　are　expected　to　facilitate　the　structural　designs　and　applications　of　the　CTS　to　flexible　composite　hinges.