In pH 4.2 HAc-NaAc buffer solution, hydroxylamine hydrochloride reduced Cu2+to Cu+that coordinate the nitrogen atom of 1,2,3-benzotriazole (BTA) to form Cu-BTA complex particles with a resonance Rayleigh scattering (RRS) peak at 369 nm. Under the selected conditions, when the BTA concentration increased, the RRS intensity at 369 nm increased. The increased RRS intensity ΔI369nmwas linear to BTA concentration in the range of 0.17-13.36 μg/mL, with a regression equation of ΔI369nm= 89.91C + 96.7, and the detection limit is 0.17 μg/mL. Accordingly, a new RRS method for BTA was established.