Abstract: AIM To determine vitamin B₁ in pharmaceutical preparations by chemiluminescence (CL) flow sensor. METHODS When 200 μL of Na₃PO₄ was passed through an anion exchange column, K₃Fe(CN)₆ was eluted from the resin and then mixed with the vitamin B₁ stream containing NaOH to product CL, by the fast oxidation reaction between vitamin B₁ and K₃Fe(CN)₆ in alkaline solution. RESULTS The CL emission intensity was correlated with the vitamin B₁ concentration in the range 1.0×10^-5 to 1.0×10^-3 mol·L^-1 and the detection limit was 8.0×10^-6 mol·L^-1 (3σ). A complete analysis, including sampling and washing, can be performed within 2 min with a relative standard deviation of less than 4.0%. CONCLUSION The vitamin B₁ flow sensor was stable for over 200 analyses and has been applied successfully to determination of vitamin B₁ in pharmaceutical preparations.