Achieving　both　light-weight　and　high-strength　cementitious　composites　(HSLWCCs)　is　challenging.　In　this　study,　hollow　glass　microspheres　(HGMs)　were　used　to　develop　a　HSLWCC.　Different　amounts　of　HGMs　were　incorporated　in　the　cement　mixture　and　the　associated　effects　on　the　engineering　properties　and　microstructure　were　investigated.　The　results　showed　that　the　density　and　strength　decreased　with　increasing　HGM　content.　Compressive　strength　of　the　HSLWCC　decreased　significantly　when　the　HGM　content　increased　from　30　to　40%　and　decreased　slightly　with　further　increasing　HGM　content,　while　the　density　generally　reduced　linearly　with　increasing　HGM　content.　Structural　efficiency　of　the　HSLWCC　increased　when　the　HGM　content　was　30%　and　then　decreased　significantly　at　HGM　content　of　40%.　In　particular,　a　floatable　cementitious　composite　with　a　density　of　~970 kg/m3　and　compressive　strength　of　~31 MPa　was　developed　by　incorporating　60%　of　HGMs.　Additionally,　two　failure　modes　(i.e.,　(i)　debonding　of　interface　and　(ii)　crush　of　HGM)　were　found　in　the　high-strength　light-weight　cementitious　composite　(HSLWCC),　with　the　former　dominating　in　HSLWCC　with　high　HGM　content　and　the　later　dominating　in　HSLWCC　with　low　HGM　content.　©　2023,　The　Author(s).