〔Abstract〕 Objective To investigate the relationship between the vasodilation and hydrogen sulfide（H2S）mecha_ nism of total flavonoids of chrysanthemum（TFCC）and the large conductance Ca2+- activated K+（BKCa）channels on vascular smooth muscle cells（VSMCs）of the middle cerebral artery in rats. In addition，this study will also in_ vestigate the effect of TFCC on the expression of BKCa channel alpha protein in rat middle cerebral artery VSMCs. Methods The primary method employed was acute digestion to isolate VSMCs from the middle cerebral artery of rats；whole-cell patch-clamp techniques were used to measure BKCa channel currents；primary tissue adherence culture was utilized to cultivate VSMCs from the middle cerebral artery of rats；Western blot were employed to de_ termine protein expression levels. Results In whole-cell patch-clamp experiments，both the H2S donor NaHS （100 μmol/L）and endogenous H2S enhanced BKCa channel currents. TFCC（30，90，and 270 mg/L）also activat_ edBKCa channels and exhibited a certain concentration-dependent effect. Even after blocking endogenous H2S production，TFCC（270 mg/L）still activated BKCa channels in VSMCs of the middle cerebral artery in rats. In Western blot experiments，the α-subunit of BKCa channel proteins was expressed in all groups of cells，but TFCC （30，90，and 270 mg/L）and inhibitor IBTX group did not affect the expression of channel protein content. Con ⁃ clusion TFCC can promote the opening of BKCa channels by promoting the generation of endogenous H2S，or di_ rectly activate BKCa channels，thereby playing a role in relaxing cerebral blood vessels. However，TFCC had no sig_ nificant effect on the expression of BKCa channel proteins.