Abstract: A new method with Cd²⁺ as the indication ion, has been established for the determination of Vitamin B1 by using square polarography. No reduction wave of V_B1 appeared in the buffer solution of NH₃-NH₄Cl. When Cd²⁺ was added to the above solution, the non-electro-active V_B1 engendered a new peak at -0.360 V. The height of the peak is directly proportional to the concentration of V_B1.The linear range of V_B1 was 1.35 μg/mL~1.35 mg/mL and the determination limit was 0.13 μg/mL,r=0.9997. The mean recoveries was 99.6%(n=9), RSD=0.9%. This method is reliable,accurate and is very suitable for the determination of vitamin B1.