Small rectangular specimens (6×6×50 mm) were chill-cast in a copper mould from molten Fe-C-Si alloys (C 0.04∼4.43%, Si 0.14∼3.65%) and molten commercial cast iron. The rate of evolution of hydrogen at room temperature from these specimens were measured by placing them in test tubes filled with mercury or in evacuated tubes. In general, the specimens containing higher carbon and silicon had considerably slower rate of evolution. The hydrogen evolution from the specimens with high carbon and silicon content was too slow to be measured by the test tubes filled with mercury, but all the specimens tested in the evacuated tubes evolved hydrogen. A 95% value period which is the time required for evolution of 5% of initially contained hydrogen was used to indicate the rate of hydrogen evolution. The 95% value period for steel, malleable cast iron and ordinary cast iron were 0.6∼2.2 hrs, 22∼70 hrs and 70∼167 hrs, respectively. A drop of temperature was effective in slowing hydrogen evolution, and the 95% value period of the specimen in ice was lengthened to about twice of that of the specimen at room temperature.