Various heat resistant alloys are being introduced for use in automobile emission equipment, such as thermal reactors and catalytic converters. For the past several years Japan has been developing alloys which emphasize oxidation resistance. Therefore, oxidation phenomena have been thoroughly researched and clarified. On the other hand, embrittlement, which is a marked deterioration similar to oxide deterioration, has not been studied sufficiently.The major subjects of investigation were the two forms of embrittlement in austenitic heat resistant alloys, caused by the precipitation of σ phase and the absorption of Nitrogen. Useful information was obtained from these results.