The deformation and fracture mechanisms in tension were studied in single-crystal Er2O3-doped ZrO2 monofilaments processed by the laser-heated floating zone method. Tensile tests were carried out between 25° and 1400°C at different loading rates and the dominant deformation and fracture mechanisms were determined from the shape of the stress–strain curves, the morphology of the fracture surfaces, and the evidence provided by monofilaments deformed at high temperature and broken at ambient temperature. The tensile strength presented a minimum at 600°–800°C and it was controlled by the slow growth of a crack from the surface. This mechanism was also dominant in some monofilaments tested at 1000°C and above, while others showed extensive plastic deformation before fracture at these temperatures. The strength of plastically deformed monofilaments was significantly higher than those which failed by slow crack growth due to the marked strain hardening capacity of this material.