Regenerable ultrafiltration membranes were fabricated via filtration of thermally-stable, highly dispersed boron nitride nanotubes (BNNTs). The highly debundled BNNTs were produced by employing judiciously-chosen poly (4-vinylpyridine) (P4VP) as an efficient steric stabilizer. Density functional theory calculations showed strong adsorption energies of P4VP monomers on top of the BNNTs, illustrating the role of P4VP stabilizers. High performance of the BNNT ultrafiltration membranes with large permeation flux was demonstrated by exclusion of polystyrene and gold nanoparticles (similar to 25 nm) with higher than 99% removal efficiency. The BNNT membranes were successfully regenerated and recycled continuously at 450 degrees C due to their excellent mechanical and thermal properties, demonstrating a stark contrast to the membranes from the carbon nanotubes. Our work indicates that unlike the membranes from carbon nanotubes, BNNT membrane can be a promising candidate for the application in cost efficient industrial ultrafiltration.