Abstract: A method of ultra-trace measurement of 2-FBA in oilfield brine is established using SPE enrichment & separation solid-phase in combination with gas chromatography- mass spectrometry (GC/MS). The method described here is rapid, accurate, and reliable for ultra-trace determination of 2-FBA in oilfield brine. The lowest detection limit of 2-FBA is 4×10 -9g/L when the 250mL sample was analyzed and the typical relative standard deviation of measurement is 10% by this method. The expanded uncertainty of a once measurement for 400ng/mL is 50 ng/mL, that means the relative uncertainty is better than 14%. The 4-methyl -fluorobenzoic (4-TMFBA) acid is used as the internal standard to modify the derivation procedure and determination by GC/MS. The range of calibration curve in the measurement by GC/MS was estimated from 5 to 2000ng/mL (R 2≥0.999 8) with internal standard calibration. It can be used in analysis of 2-FBA in other samples such as environ-mental, biological and drug samples. The work makes also the base for analysis of other FBAs in oilfield brine when used as waterflood tracers in future.