Flexural, tensile, and high cycle fatigue test data are presented for pressureless sintered aluminium nitride (AIN) and hot-pressed aluminium nitride reinforced with silicon carbide whiskers (SiCw/AIN). Tests were conducted at ambient temperature. The SiCw/AIN composites consisting of 30wt% SiCw produced significant increases in flexural strength, tensile strength, and tensile fatigue strength compared to monolithic AIN. Increases were nearly double in all cases. Corresponding strain-to-failures measured in tensile tests increased from ∼ 0.04% in monolithic AIN to ∼ 0.10% in the SiCw reinforced composite. Fracture surfaces showed evidence of whisker-toughening mechanisms due to additions of SiCw whiskers. High-cycle fatigue results indicated that both materials have the ability to sustain higher stress levels in the cyclic tests compared to the tensile experiments. The improved performance under cyclic testing is explained in terms of strain-rate effects. The times at or near peak stress are considerably less under high-cycle fatigue testing (20 Hz) compared to tensile tests (strain rate = 0.5%min−1).