The replica-method for the microscopic examination has been studied. A certain part of the material to be examined is etched after polishing, and then it is electrochemically plated dy dropping metallic salt solution, which is electrochemically nobler than the sample, or its acidified solution with hydrochloric acid. This plated sample is pasted on a celluloid plate wih its plated metal by amylacetate. After dried up, the celluloid is torn off from the mother metal. And the plated metal is separated from its mother metal and remained on the celluloid plate. Thus the aimed replica is accomplished, and it is satisfactory to be examined under the microscope.Tested materials are shown on Table 1, and salts used in the chemical plating are Cu(NH4)2Cl4·2H2O and CuCl2·2H2O. The composition of this plating solution for replica is shown on Table 2 to Table 4, A, H, T, N, R and C in the 2nd column of the tables show annealing, hardning, tempering, normalizing, rolling and casting, respectively.The materials, which can be etched by 5 per cent nitric acid-alcohol solution or 5 per cent picric acid-alcohol solution, can be reproduced by the plating solution shown in Fig. 1 and Fig. 2 for replica. But, for the austenite structure, the volume of hydrochloric acid is always fixed to the maximum value, and only the concentration of Cu(NH4)2Cl4·2H2O is changed in accordance with the carbon contents.Photo. 1-a to Photo. 5-a are the ordinary ones of the structure of malleable cast iron, mild steel, eutectoid steel, high manganese steel and high speed steel, respectively, and Photo, b and c are the photographs of the replica of these materials. In the Photo. 4-b, because of the plating solution being dilute, the carbides were not replaced with Cu ion chemically, and therefore, they seemed dark, dut Photo. 4-c, by raising the concentration, they were replaced chemically and the result was white Photo. 5-b is the case of duble carbides, which it is difficult to replace chemically, and dark in the cores.