The effects of water subjected to an electromagnetic field on the fracture parameters and mechanical properties of self-compacting lightweight concrete (SCLC) were investigated. The test variables were the magnetic field intensity (MFI) used to treat the water and the water/cement (w/c) ratio. Eight mix compositions with various MFIs and two w/c ratios (0·37 and 0·42) were considered. For each w/c ratio, the nominal maximum aggregate size and all mix designs were constant, while four magnetic fields were considered. Three-point bending tests were conducted on 96 notched beams and the results were analysed by means of the size effect method. Satisfactory results were achieved in terms of the fracture parameters and the mechanical properties of the SCLC. By increasing the MFI, the results indicated that: (a) the mechanical properties, initial fracture energy and fracture toughness increased at different rates, which can be attributed to the positive effects of the magnetic field on water clusters; (b) the effective length of the fracture process zone increased, illustrating an improvement in ductility of the SCLC specimens; (c) the desired design criterion of the SCLC samples approached the strength criterion.