Sodium combustion tests were performed to investigate both the pool burning behavior and the maximum temperature of a steel-made floor liner in the case of small-scale sodium leakage from a secondary loop of a fast breeder reactor. Sodium leakage heights, humidity in an atmosphere and sodium leakage rate were changed as parameters in the tests. This paper mainly described thermal influence to the steel liner. Main conclusions are as follows. The maximum liner temperature becomes higher with the increase in the leakage height and humidity. When the leakage rate decreases, the maximum temperature tends to become lower, and this behavior has the relation with final pool size that affects to heat release toward radial direction. Sodium leakage rate has no dependency on the sodium burning rate and pool expanding speed while it affects to the final pool size. The surface shape of sodium combustion pool has influence on both the pool expanding speed and the final pool size.