Objective T o establish a gas chrom atography-m ass spectrom etry (G C-M S ) m ethod for the determ ination of sulfide ion in blood and apply it to the practical cases. Methods T he 1, 3, 5-tribro-m obenzene w as selected as an internal standard, and 0.2 m L blood sam ple w as collected and analyzed using G C-M S after α-B rom o-2, 3, 4, 5, 6-pentafluorobenzyl brom ide derivatization. Results T he m ass concentration of sulfide ion in blood had good linearity in the range of 0.2-40μg/m L w ith a lim it of detection (L O D ) of 0.05μg/m L . T he m ass concentration of sulfide ion w as less than 0.05μg/m L in blank blood from different sources such as healthy subjects and dead cases. In 3 sulfide poisoning cases, sul-fide ion w as detected in the blood sam ples of 6 victim s, and the m ass concentration range w as 1.02-3.13μg/m L . Conclusion T his study establishes a m ethod for investigation of sulfide ion in blood w hich has been applied successfully to the cases of fatal sulfide poisonings.