This paper investigates experimentally and numerically the biaxial flexural behaviour of thin circular slab specimens made of Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRC). The circular slab specimens represent an external tensile reinforcement layer for reinforced concrete (RC) slabs or a new thin slab element, for the application, e.g. in bridge construction. The ring-on-ring test method has been developed to measure the equi-biaxial strength and deflection of the specimens. The 3-D deformation field and crack development on tensile surface are recorded continually using Digital Image Correlation (DIC). The experimental results validate the ring-on-ring test method, allowing for the consideration of the stochastic nature of UHPFRC. Significant flexural and deformational capacities of UHPFRC slab under biaxial condition are highlighted. Furthermore, 3-D non-linear finite-element analysis (FEA) accurately simulates the structural behavior of the tested slabs.