Bending behaviour of members without ordinary reinforcement made of quasi-brittle materials (such as concrete or fibre-reinforced concrete) is subjected to size effect both in terms of strength and ductility. For a typical ultra-high performance fibre-reinforced concrete (UHPFRC), size effect on bending strength is less significant. In this paper, taking advantage of an analytical approach, this behaviour is confirmed if large tensile strains are developed in UHPFRC before beginning of tension softening. However, it is also shown that changes in the size of the member have a significant influence on the ductility in bending. Both results are in agreement with available experimental data. A parametric study on size effect in bending is finally performed by varying the tensile strain before beginning of tension softening and the initial slope of the tension softening law. On that basis, some considerations on the modelling and design of such members are given.