For the micro-morphological study of diseased root surface in situ, the use of an accurate and reproductive replica technique is essential if object under study cannot be observed directly. Before taking the impression, the surface was irrigated with saline solution, dried with air jet. Primary replica is taken by application of silicone rubber impression material into periodontal pocket. Epoxy resin is poured into hardened impression material to obtain secondary replica, and this secondary replica plated with platinum was used for the observation with scanning electron microscope (S.E.M.). The replica surface reproduced accurately the tooth except in the areas near the bottom of pocket, where the close proximity of epithelium and cementum hindered the insertion of impression material making observation impossible. This technique offers possibilities of the micro-morphological study of diseased root surface in situ.