A new GCMS-based method for quantitative determination of active substance of new contrast drug based on sulfur hexafluoride (SH) in the rat blood plasma is produced. A ratio plot of peak area of sulfur hexafluoride to peak area of internal standard toluene [y, S(SH)/S(toluene)] versus concentration of sulfur hexafluoride (x, µL/mL) was linear over 0.003-0.500 µL/mL. The calibration graph can be described by the equation y=0.9526x+0.0037 (r2=0.9990). Limit of quantitation (LOQ) (signal-to-noise 10,12) was 0.003 µL/mL. Inter- and intra-serial accuracy related to nominal concentrations were 100.40-101.20% and 86.67-110.0%, respectively. The RSD values for inter- and intra-serial accuracy were 3.68-4.15% and 1.23-10.68%, respectively. The samples of the same series with SH concentrations 0.01 µL/mL and 0.50 µL/mL were analyzed in order to determine the stability. Samples were stored for 24 hours to determine the short-term stability. To determine the long-term stability Samples were stored for 25 days. Short-term stability at room temperature were 0.52% and 1.86% and long-term stability at -20 °C were -90.43% and -81.81% for SH concentrations 0.01 µL/mL and 0.50 µl/ml, respectively. Accuracy during freezing and thawing of samples were 102.30% and 100.10% and RSD values were 5.40% and 1.50%, respectively.