Abstract: In Tris-HCl buffer solution of pH 6.38 and in the presence of hexadecylpyridinium bromide,vitamin B₁ reacts with chlorophenol red to form a new complex, leading to a significant enhancement of resonance Rayleigh scattering, and giving a new resonance Rayleigh scattering spectrum. The resonance Rayleigh scattering peak was found to locate at 339 nm. Linear relationship between values of resonance Rayleigh scattering intensity (ΔI_RRS) and mass concentration of vitamin B₁ was kept in the range of 0.03-0.42 mg·L^-1, with detection limit (3s/k) of 0.004 2 mg·L^-1. Based on these facts, resonance Rayleigh scattering method for determination of vitamin B₁ in pharmaceuticals with hexadecylpyridinium bromide as sensitizer was proposed. The proposed method was applied to the analysis of vitamin B₁ pharmaceuticals, giving values of recovery and RSD's (n=6) in the ranges of 99.2%-102% and 2.1%-2.5% respectively.