Atomic force microscopy (AFM) was used to determine the atomic configuration and topography of the surface of KMn8O16, a powdered form of alpha-manganese dioxide (alpha-MnO2) containing K ions, By depositing the powder on mica, we were able for the first time to use AFM to image the surface of the powder. We took three types of images : low-resolution, wide-scan (5 x 5 mu m(2) region); high-resolution (500 x 500 nm(2) region); and atomic-scale (10 x 10 and 2 x 2 nm(2) regions). The low-resolution imaging showed that the powder has needle-like crystallites. The high-resolution imaging showed that the surface of the powder has a "faceted" structure, The atomic-scale imaging revealed that the facet plane has a hill-and-valley structure with a height difference of 0.2-0.3 nm along the crystal C axis, Furthermore, the surfaces of the hills were (110) surfaces, and those of the valleys were surfaces formed by the removal of O-Mn-O units from these (110) surfaces, Atomic-scale imaging of a hill shows a periodic structure that corresponds to the configuration of surface hydroxyl species and bridging oxygen atoms of the (110) plane, The close agreement that we found when we superimposed the atomic-scale images and the bulk structure projection indicates that there is no reconstruction on the (110) surface of powdered KMn8O16.