Abstract: An isotope dilution internal standard-ultra-high performance liquid chromatography-tandem mass spectrometry method was proposed for determination of 9 commonly illegally added glucocorticoids in antibacterial cream products, including betamethasone valerate, betamethasone dipropionate, beclomethasone, betamethasone, beclomethasone dipropionate, clobetasol, betamethasone acetate, clobetasone butyrate, and clobetasol propionate. 0.200 g of the sample was taken into a 15 mL-centrifuge tube, followed by the addition of 100 μL of the mixed isotope internal standard stock solution containing 2.0 mg·L⁻¹ of betamethasone-d₅, betamethasone acetate-d₃, beclomethasone dipropionate-d₁₀, clobetasol propionate-d₅, beclomethasone-d₅, and clobetasol-d₅.The analytes were extracted with 5.0 mL of acetonitrile by vortex, followed by the addition of 1.0 mL of acetonitrile-saturated n-hexane and 1.0 mL of saturated sodium chloride solution. The mixture was vortexed for 2 min, subjected to ultrasonic extraction for 20 min, vortexed again for 15 min, and allowed to settle for 20 min, and then the upper n-hexane layer was discarded. 1.5 mL of extract in the middle acetonitrile layer was transferred into a centrifuge tube, frozen at −20 ℃ for 2 h, and the upper layer was discarded. An aliquot of the frozen acetonitrile extract （0.75 mL） was diluted with 0.75 mL of water, vortexed, mixed, frozen again at −20 ℃ for 2 h, and centrifuged at 4 ℃ for 5 min. The resulting supernatant was filtered through a 0.22 μm-PTFE membrane, and 9 glucocorticoids in filtrate were separated on Acquity UPLC^® BEH C₁₈ column using the mixtures of 0.1% （volume fraction） formic acid solution and acetonitrile at different volume ratios as the mobile phases for gradient elution. The separated targets were scanned using electrospray ionization source in positive ion mode, detected in multiple reaction monitoring mode, and quantified by the internal standard method. As shown by the results, the standard curves for 9 glucocorticoids showed good linearity in the range of 0.50−80.0 μg·L⁻¹, with detection limits （3S/N） in the range of 0.9−7.5 μg·kg⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 75.7%−112%, with RSDs （n=6） of the determined values in the range of 1.3%−15%. This method was applied to the analysis of 110 batches of antibacterial cream products collected in Fujian Province. It was shown by the results that glucocorticods were detected in 26 batches of samples, with the detection rate of 23.64%（26/110）, including clobetasol propionate, betamethasone dipropionate, clobetasone butyrate, and betamethasone, and the detected amounts were 0.289−332.121 mg·kg⁻¹, 0.308−0.312 mg·kg⁻¹, 0.301 mg·kg⁻¹, and 0.337 mg·kg⁻¹, respectively.