This paper explores the effectiveness of boron nitride nanosheets in preventing the premature failure of yttriastabilized tetragonal zirconia ceramics, particularly in humid environments. A simple, low-cost and scalable technique-shear exfoliation in a kitchen blender-was used to prepare BNNS, and pure zirconia and composites with 1, 2.5 and 5 vol. % BNNS were spark plasma sintered. Accelerated hydrothermal ageing experiments in autoclave revealed a remarkable improvement of low temperature degradation resistance in all the composites. Fracture toughness and slow crack growth of the composites with 1 and 2.5 vol. % BNNS were evaluated by bending tests performed in notched specimens. Although the composites presented fracture toughness values similar to those of the reference zirconia, an increase of similar to 18 % on crack-tip toughness was achieved. Similar Rcurves evaluated in air and in oil-impregnated 2.5 vol. % BNNS composites revealed a limitation of stress-assisted corrosion by water in zirconia, thanks to the BNNS incorporation.