Chiral　metasurfaces　with　high　quality　factors　(Q-factors)　are　a　promising　platform　for　achieving　chiral　optical　responses.　However,　the　optical　properties　of　most　metasurfaces　are　fixed　once　they　are　fabricated.　Here,　we　study　the　effect　of　phase-change　material　Ge2Sb2Te5　(GST)　on　the　chiral　optics　of　a　planar　chiral　Si　metasurface　driven　by　bound　states　in　the　continuum　(BICs),　as　the　refractive　index　of　the　phase-change　material　changes　before　and　after　the　phase　change.　The　planar　chiral　silicon　metasurface　is　capable　of　generating　near-unity　(0.99)　circular　dichroism　and　giant　(0.996)　linear　dichroism　in　the　infrared　region.　Notably,　phase-change　material　GST　is　integrated　into　the　Z-shaped　Si　metasurfaces.　We　actively　tune　the　dissipative　loss　by　causing　the　GST　to　undergo　a　phase　transition,　thereby　modulating　the　optical　chirality.　In　addition,　we　numerically　simulate　the　effect　of　the　thickness　of　the　phase-change　layer　and　the　embedded　position　on　the　optical　response.　Compared　with　single-functional　metasurfaces,　this　device　exhibits　better　flexibility　and　more　functionalities.　It　is　demonstrated　that　the　optical　chirality　of　the　metasurface　can　be　well　controlled　using　the　phase-change　material　GST.　©　2024　Optica　Publishing　Group.　All　rights,　including　for　text　and　data　mining　(TDM),　Artificial　Intelligence　(AI)　training,　and　similar　technologies,　are　reserved.