In this study, a new cement-based composite with high early strength and toughness was developed by the addition of micro-fine steel fibre (MSF) in sulphoaluminate cement (SAC). The new composite is termed as MSF reinforced SAC composite (MSFRSC). The mechanical behaviour of MSFRSC was experimentally investigated, the flexural toughness and ductility of MSFRSC was evaluated. It was found that the compressive strength, flexural strength, shear strength, flexural toughness and ductility of MSFRSC were significantly influenced by the curing time and volume fraction of MSF. The compressive strength, flexural strength and shear strength of MSFRSC increased with the increase of curing time, especially during the first three days. The flexural strength and shear strength of MSFRSC improved significantly with the increase of the volume fraction of MSF. The flexural toughness of MSFRSC significantly improved and the ductility slightly improved with the increase of the volume fraction of MSF from 0.0% to 2.0%. The flexural toughness slightly increased and the ductility slightly decreased with the increase of the curing time from 1 day to 28 days. Also, the recommendations of different codes for the evaluation of the flexural toughness and ductility of MSFRSC were compared. The recommendations in ASTM C1609 fully reflected the flexural toughness and ductility of MSFRSC. The recommendations in JG/T 472-2015 distinguished the influence of MSF on the pre-peak and post-peak flexural load-deflection behaviours of MSFRSC. A simplified approach based on JG/T 472-2015 was proposed to evaluate the flexural ductility of MSFRSC.