In this study, the flexural behaviour of thin micro-steel fibre of low specific gravity was evaluated. Micro-steel fibre has higher strength, toughness, and elasticity than conventional steel fibre. Flexural tests were carried out using 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, and 1% fibre volume fractions ( V f). The flexural strength and flexural toughness of micro-steel fibre-reinforced cement composites were superior to those of steel fibre-reinforced cement composites. Flexural strength increased by 20%, 37%, 33%, 41%, 47%, and 48% in micro-steel fibre-reinforced cement composites with 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, and 1% V f, respectively, compared with steel fibre-reinforced cement composites of the same V f. The 0.2% and 0.3% volume fractions did not significantly affect flexural toughness. However, flexural toughness increased by 39%, 56%, 44%, and 36% in amorphous steel fibre-reinforced cement composites with 0.4%, 0.5%, 0.7%, and 1.0% V f, respectively, compared with steel fibre-reinforced cement composites of the same V f.