Continuous carbon fibre ceramic matrix composites capable of tolerating multiple thermal-shock cycles and resisting ablation are needed for aerospace and hypersonic systems. Carbon fibre around 50 vol% and ultra-refractory matrices are fundamental parameters. The influence of rare earth (RE) oxides on the microstructure and mechanical properties of carbon fibre-ZrB2/SiC composites was investigated. Materials were produced by slurry infiltration and hot pressing. The addition of Y2O3, La2O3 and CeO2 led to the formation of lamellar boro-carbides that improved the densification, while Sc2O3 promoted the formation of (Zr,Sc)B2 solid solutions in the matrix. All these composites exhibited improved mechanical properties compared to a RE-free baseline, with room temperature strengths and toughness above 330 MPa and 9 MPa m0.5, respectively, and strengths above 600 MPa at 1500 °C. The lamellar phase …