In this paper, an outline of mean-field homogenization and fracture toughness of boron nitride nanotube-reinforced aluminium and epoxy composites have been presented. The meso-scale material modelling has been achieved using Mori-Tanaka and double inclusion homogenization schemes. To examine the effectiveness of Mori-Tanaka and double inclusion schemes, a comparison has been drawn with the rule of mixture. Meso-scale numerical results of boron nitride nanotube-reinforced aluminium and epoxy composites are presented for various design parameters such as aspect ratio and volume fraction of boron nitride nanotubes. The validation studies of the developed transversely isotropic composites model have been documented with the experiments performed and existing literature. Finally, macro-scale fracture toughness simulations incorporating the transversely isotropic properties have been performed using the domain integral method. It is observed that aluminium and epoxy with elastoplastic and viscoelastic nature, respectively, have shown a significant effect on the fracture properties of the composites. © IMechE 2020.