[en] The corrosion behavior of core materials in lead cooled reactor was investigated as the feasibility study for fast breeder reactor. The results are summarized as follows. 1. The corrosion of stainless steels under lead and lithium occurs mainly due to the dissolution of nickel. Consequently ferrite stainless steels have better resistance to corrosion under lead and lithium than austenitic stainless steels, and the corrosion resistance of high nickel steels is worst. 2. The dissolution rate, D (mg/m²/h), is correlated with lead and lithium temperature, T(K), as log₁₀ Da=10.7873-6459.3/T and log₁₀ Df=7.6185-4848.4/T, where Da is the dissolution rate for austenitic steels and Df is for ferritic steels. It's possible to calculate the corrosion thickness, C (μm), using the following correlation: C=(Dxt)/ρx10^-3, where t is exposure time (hr) and ρ is density of the core material (g/cm³). 3. The corrosion thickness estimated for austenitic steels using above correlations was extremely larger than ferritic steels, about 6 times at 400 degC and more than 20 times at above 600 degC. It's considered that applicable temperature in lead cooled reactor core is below 400degC (about 60 μm corrosion thickness after 30000 hr) for austenitic steels, and below 500degC (about 80 μm after 30000 hr) for ferritic steels. (author)