This is to report a part of the research work presently engaged to analyze the relationship between the blow hole formation and the gas evolution originated in the cores, which will also help to find the core binder bringing the least effect on the blow hole formation. The experiment has been carried out in the study of the phenomenon connected with the gas evolution from cores which were subjected to heat. In the experimental work, two methods have been applied. One is to use Elema furnace (1,200°C) with silica tubes (Experiment A), and the other is to use molten cast iron (1,350°C) with steel pipe (Experiment B). The measurement has been recorded in the gas evolution rate (c.c./sec) rather than in the total gas volume (c.c.). The materials applied in the testing cases were domestically produced phenolic resin, urea resins, linseed oil and phenolic resin of the U. S. product. No practical results have been obtained in the experiment A because of the low temperature of the furnace and the low heat conductivity of the silica tube. Experiment B brought better results, though it has yet been unable to determine which binder brought the highest effect on the blow hole formation. Up to the present it has been made clear that the U. S. phenolic resin brought the less effect on the blow hole formation than the domestic linseed oil.