PROBLEM TO BE SOLVED: To provide a tail seal composition less in combustibility and concern to environment.SOLUTION: There is provided a tail seal composition for shield boring machine containing [A] a lubricant base oil consisting of carboxylic acid ester of aliphatic alcohol of 20 to 50 mass%, [B] a pyrolytic powder body of 10 to 50 mass%, [C] inorganic powder body of 20 to 60 mass% and [D] fiber of 2 to 10 mass% and having the flash point of the lubricant base oil of 240°C or more.SELECTED DRAWING: None