This contribution is focused on the optimal fibre content in the ultra-high performance fibre reinforced concrete (UHPFRC) mixture with respect to the residual velocity of the non-deformable projectile after perforating the UHPFRC slabs. Impact velocity of the non-deformable projectile was in the range of 700 m/s. The UHPFRC used in this study exceeded 150 MPa in uniaxial compression and tensile strength was around 10 MPa. In total 24 UHPFRC slabs with different fibre content were tested for impact loading. In addition, 8 slabs were tested for comparison including high strength concrete (HSC) and conventional fibre reinforced concrete (FRC). It was verified experimentally that UHPFRC had an excellent impact resistance compared to conventional materials such as FRC or HSC. Further it was found that optimal fibre content in UHPFRC for impact resistant structures is 2% by volume. Usage of less than 2% of fibre concrete by volume led to higher residual velocity of the projectile after perforating the slab and also to higher debris fragment mass.