Crystalline organic frameworks incorporating dative B←N and reversible B─O bonds (BNOFs) have garnered increasing interest on account of their crystallinity, porosity, and processability. However, strategies for introducing functions into BNOFs remain largely unexplored. In this work, a series of functionalized BNOFs, named BNOF-n (n = 2–9), have been designed and synthesized using a mixed-monomer assembly strategy. The obtained materials share structural similarities but reveal distinct functional groups, demonstrating excellent chemical stability, high surface areas, and remarkable regenerability. Notably, BNOF-5, functionalized with abundant carboxyl groups, achieves exceptional reversible NH₃ adsorption capacity (up to 10.0 mmol g⁻¹ at 1 bar and 298 K), significantly surpassing that of the nonfunctionalized BNOF-1 (5.6 mmol g⁻¹) and the less-functionalized BNOF-7 (7.9 mmol g⁻¹), thereby clearly demonstrating the effectiveness of the functionalization strategy. Remarkably, the damaged BNOF-5 can be efficiently repaired through facile regeneration, highlighting its outstanding recyclability. This work demonstrates the first attempt at functionalization methodology in BNOFs, extending their potential toward diverse applications.