This study reports experimental and numerical studies on the flexural behaviour of sustainable fibre reinforced lightweight hollow core slabs (FR-LWHCS). An innovative and sustainable LWHCS is proposed for structural applications using a lightweight concrete mix of 1800 kg/m3 density, previously developed by authors. Full-scale precast LWHCS specimens are cast and tested under flexure using a four-point loading configuration. A high shear span to depth (a/d) ratio of 10 is chosen to have flexure dominant behavior. FR-LWHCS is made using sintered fly ash aggregate (SFA) as coarse aggregate and monofilament macro synthetic fibres of different volumetric fibre dosages (0.4 % and 0.6 %). A small dosage of micro synthetic fibres of 0.02 % by volume is also added to arrest shrinkage cracks. Two control slabs, one constructed with lightweight concrete and the other with conventional normal density concrete, are tested. The digital image correlation (DIC) technique is used to track the cracks and failure modes. A 3D finite element analysis is performed to supplement the test results. Test results show that FR-LWHCS satisfies all the structural requirements, leading to economy and sustainability. FR-LWHCS with 0.6 % fibre dosage performed better than hollow core slabs made of normal density concrete. Though the addition of fibres did not considerably increase peak load, a minimum dosage of fibre addition is warranted in LWHCS to improve the serviceability performance. Fibre addition significantly improved the strain energy absorption. © 2023 Elsevier Ltd