Molecular-resolution images by atomic force microscopy (AFM) revealed a reversible ordering-disordering transition of molecular arrangements on the (010) face of a single crystal of potassium tetracyanoplatinate bromide (KCP(Br)) during dehydration and hydration treatments. The intracolumnar Pt-Pt distance along the c-axis in the dehydrated crystal lengthens by a factor of 30% with considerable disordering, and the rehydrated crystal shows well-ordered arrangement like the as-grown crystal, while the intercolumnar structure along the orthogonal direction is not varied. Large-scale AFM images showed that the monolayer terraces reversibly slide in the c-axis direction during the dehydration-hydration treatments, reflecting the molecular dislocation along the c-axis. This surface structural change is quite consistent with well-known dehydration effects in KCP(Br) crystals, i.e., the lattice disordering and the decreasing conductivity.