The purpose of this study was to observe the effect of cleansing action of irrigation solutions which was 3% $H_2O_2$ and 5% NaOCl, and 15% EDTA solution on the root canal wall. After treatment with the irrigant, each sample was dehydrated, and coated with 200~250${circ}$A of gold, and observations were made with the use of scanning electron microscope. The results were as follows: 1. In the root canal walls irrigated with 3% $H_2O_2$ and 5% NaOCl solution without instrumentation after extirpation through barbed broach, the predentin of root canal wall was found scarely affected, and the wall was shown retaining network structure and fibrous organic matters. 2. When 15% EDTA was applied as irrigants for 60, 90 and 120 seconds after instrumentation, there was no signigicant difference of the cleansing effect of the elapsed times which were 90 and 120 seconds on the root canal wall, but in the applied time which was 120 seconds, the canal wall was the cleanest. Therefore it was thought that the most suitable application time of 15% EDTA as the irigants was 120 seconds.