A variety of borylborazine-based polymers were successfully converted into boron nitride fibres via the preceramic polymer route. In this procedure, four monomers were polycondensed into highly tractable polymers which could be easily melt-spun into fine-diameter green fibres. These polymeric filaments were then transformed into boron nitride fibres after a well-defined heat-treatment at 1800 °C in a controlled atmosphere. All the resulting ceramic fibres were mechanically tested. In particular, results showed that the promising mechanical properties for two of the polymer-derived fibres were closely related to the structural units of the corresponding preceramic polymers.