We investigated the role of hydrogen sulphide (H 2 S) in intracellular pH (pH i ) regulation in vascular smooth muscle cells and its contribution on vasodilation. NaHS, a H 2 S donor, decreased pH i in a concentration-dependent manner ranging from 10μM to 1mM. Neither inhibition of the Na + /H + exchanger with 5-(N-ethyl-N-isopropyl) amiloride, (EIPA, 10μM), nor plasmalemmal Ca 2+ -ATPase with CdCl 2 (20nM) alters the effect of NaHS on pH i . Blockade of the Cl-/HCO3- exchanger with 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) significantly attenuated the pH i lowering effect of NaHS. Moreover, NaHS significantly increased the activity of Cl-/HCO3- exchanger when measured with NH 4 Cl prepulse method. DIDS attenuated the vasorelaxation induced by NaHS whereas EIPA and CdCl 2 did not cause any change. In conclusion, H 2 S induced intracellular acidification via activation of Cl-/HCO3- exchanger, which is, at least partially, responsible for H 2 S-mediated vasorelaxation.