Given the superior thermal stability and microwave transparency features, continuous BN fibers have displayed great potential to fulfill the increasing demand for high‐temperature structural and functional materials. The performance of BN ceramic fiber depends heavily upon its composition and microstructure. Herein, nearly stoichiometric BN fibers with high crystallinity were achieved through a facile boron trichloride (BCl3) assisted curing process. The fibers achieved a boron/nitrogen element ratio of 0.996:1 with increasing the degree of curing. After subsequent heat treatment, the fibers had uniform elemental distribution and h‐BN crystal structure. Compared with pure NH3 curing, the BN fibers cured with BCl3 demonstrated higher crystallinity (92.35%) and consistent orientation (79.8%). The existing state changes of elements revealed BCl3 assisted curing process could evenly disperse B atoms into the precursor fibers to fill the vacancies caused by nitrogen enrichment. These insights improve our understanding of preceramic fibers treatment for exploiting high‐performance BN ceramic fibers.

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