Objective To establish a new inhibitory kinetic spectrophotometric method for the determination of trace Sb3+ in water sample. Methods A new inhibitory kinetic spectrophotometric method for the determination of trace Sb3+ was established based on the inhibitory effect of Sb3+ on the oxidation of thionine by H2O2 in a buffer solution of NH3-NH4Cl at pH=10.50. Results The linear range of this method was 0.004-0.40 ?g/ml, r=0.999 2,the limit of detection was 1.71?10-3 ?g/ml, and RSDs were 1.4%～ 2.1% , the recovery rates were 96.2% -101.9% . Conclusion This method is accurate, fast, simple and applicable to the determination of antimony content in environment water samples.