Pb(1 0 0) and Pb(1 1 1) single crystals in 50 mM H2SO4 aqueous solution have been investigated by in situ electrochemical atomic force microscopy (EC-AFM) under potential control. We have succeeded in observating high resolution images of Pb(1 0 0) and Pb(1 1 1) single crystals, as well as high resolution and morphological images of PbSO4 crystals formed on the Pb single crystals. We found that the top face of PbSO4 crystals formed on Pb(1 0 0) is PbSO4(0 0 1), while that on Pb(1 1 1) is PbSO4(1 0 0). We also found that the atomic rows along the [1 0 0] and [0 1 0] direction of PbSO4(0 0 1) surface were parallel with those along the [0 1 1] and [0 1 (1) over bar] direction of the Pb(1 0 0) substrate, while those along the [0 1 0] and [0 0 1] direction of the PbSO4(1 0 0) surface were parallel with those along the [0 1 (1) over bar] and [(1) over bar 1 1] direction of the Pb(1 1 1) substrate.