Abstract: <DIV>A method for the determination of micro amount of iodide ions in water sample by the derivable gas chromatography has been developed.In the H2SO4 acid medium，iodide ions were oxidized by K2Cr2O7，the iodine formed reacted with 2-butanone in acid medium to give 3-iodo-2 butanone that extracted by cyclohexane，then the iodide ions in water sample were determined by gas chromatography.The result of this method (38.62 mg/L) was basically in accord with that of ion selective electrode method (37.16 mg/L) and NaNO2 oxidation-spectrophotometry (37.50 mg/L).The butanone derivative gas chromatography has the advantages of less water sample （1.0 μL）and higher degree of accuracy（10-3 μg/mL）.</DIV>