Nanoparticles of a borate nonlinear optical material, K3B 6O10Br (KBB), have been fabricated and demonstrated excellent catalytic activity in UV-induced dechlorination of chlorophenols, which are typical persistent organic pollutants. The obtained dechlorination efficiency is 2 orders of magnitude higher than that of a commercial P25 TiO2 catalyst under UV (λ > 254 nm) light irradiation. The noncentrosymmetric structure of KBB gives rise to an intrinsic large polarization effect as evidenced by Kelvin probe force microscopy, and the polarization promotes separation of photogenerated electron-hole pairs, leading to efficient cleavage of chlorophenols into small molecular fragments and dissociative Cl^- anions. This work suggests that nonlinear materials open a new window for designing efficient photocatalysts.