Background/Aims: Helicobacter pylori (H. pylori) is unique in its ability to persist in acidic environment. The main mechanisms to survive in low pH are to produce large amounts of urease and to have ATPases. This study was performed to invetigate the characteristics of ATPases of H. pylori. Methods: ATPase activity of microsomes prepared from H. pylori (ATCC 43504) was measured by enzyme-coupled assay. The effects of pH, sodium azide (NaN3), N,N-dicyclohexylcarbodiimide (DCCD), diethylstilbestrol (DES) and bafilomycin on the microsomal ATPase activities were determined. We also investigated the effect of nigericin on the ATPase activity. Results: The ATPase showed maximum activity at pH 5.5. The activitiy was decreased by 29%, 38% and 42% with the addition of NaN3, DCCD and DES, respectively. Bafilomycin had little effect on the ATPase activity. ATPase activity was decreased with the addition of DES dose-dependently, while it was increased by nigericin dose-dependently. Conclusions: These results suggest that cell membrane of H. pylori possesses two types of proton pumps, F-type and P-type ATPases, which act as H+ ATPase.