In order to investigate some preventive measures against the oxidation of silicon carbide refractories the sintered specimens of fine SiC powders bonded by Kibushi clay, a popular binder in Japan, were heated at 1175°-1450°C for 50-100 hours in the current of dry oxygen to measure the weight increase, apparent porosity, length and the expansion up to 500°C. The results were compared with those obtained with the bondless bodies formed by adding a small amount of Syton 2X, a silica gel preparation. They weres ubjected to oxydation under the same conditions (as before).Based on the following experimental results, and on some additional considerations the author advanced a tentative plan of improving the characteristics of clay bonded refractories.(1) The bondless body used in this experiment was liable to oxidation with a large volume change. But, at the temperatures higher than 1400°C a small amount of impurity promoted remarkably the lowering of apparent porosity during the process of oxydation, so that the oxydation itself was held back to some degree.(2) Sintered body with 15-30% Kibushi clay as binder showed only a small volume change after long hour's heating at 1300°-1350°C or higher, because of the slow rate of oxidation. At a lower temperature (1175°C) the crystallization of the oxidation product, SiO2, and the influence of cristobalite liberated from the clay were corelative to show a larger expansion than bondless bodies. At higher temperatures (above 1400°C) a melt of low viscosity came out from the body making the surface more porous. The author concluded that the increase of clay substance gave practically no merit of preventing the oxidation of SiC. Taking into other important points the amount of clay should be as low as possible.(3) Kibushei clay used as bond failed to prevent the oxidation at the temperatures lower than about 1230°C. The bodies of low porosity produced by maturing sufficiently at a temperature higher than 1450°C the material added by the components such as Na2O and K2O, which effectively glassify SiO2, may be expected to improve the defects at least to some degree.