Due to their excellent mechanical properties, nanoparticles have great potential as reinforcing phases in composite materials, friction modifiers in liquid lubricants, catalysts and drug-delivery agents. In the present study, the mechanical analysis of individual spherical hollow BN nanoparticles (BNNPs) using a combination of in situ compression tests inside a high-resolution transmission electron microscope (TEM) and theoretical modelling was conducted. It was found that BNNPs display high mechanical stiffness and a large value of elastic recovery. This enables the hollow BNNPs to exhibit considerably large cyclic deformation (up to 30% of the sphere's original external diameter) and to accumulate plastic deformation of approximately 30% of the total compression strain. Theoretical simulations allowed for elucidation of BNNPs' structural changes under compression at the atomic level and explained the origin of their high stiffness and large critical deformation values.