Cleaved surfaces of K⁴Nb₆O₁₇·3H₂O, a layered compound with two different interlayer structures, were observed with Atomic force microscope (AFM). Comparison of the atom-resolved images with the crystal structure clearly showed that there are two different ways of cleavage. The more flexible but weaker interlayer was broken in a 'slow' cleavage with application of a very weak tensile force, while the stronger and more rigid interlayer was mainly broken in a 'rapid' cleavage with an excessive force. In estimation of cleavability, dynamic factors must be taken into account in addition to static parameters.