Abstract: Under γ irradiation of TBP-n-dodecyl-nitric acid system,the "do-bads" is formed,which seriously interferes in separation of nuclear fuel from fission products and is difficult to wash out. The constituents of the "do-bads" have been studied with the chemical method,IR spectrum and MS. It is found that the "do-bads" is a mixture of long chain acid phosphate ester,oligomer of phosphate,and nitro,nitroso, nitric acid ester of tributyl phosphate. The nitro, nitroso and nitric acid ester groups can be added