Abstract: In the safeguards environmental sampling, analyzing isotopic ratio of single uranium-bearing particle in swipe samples was very important. For this purpose, fission track (FT) technique was successfully applied in combination with thermal ionization mass spectrometry (TIMS). An improved FT-TIMS analysis method was developed. The particle was suspended in the solution of collodion commixed with isoamyl acetate and then spread onto a glass surface, and the solution was dried to form a polycarbonate film. After irradiation and etching, and the film containing uranium-bearing particles could be found and located under the help of microscope; a small part of the film contained one uranium particle was then cut and transferred on a Re filament of TIMS. The isotopic ratio of the particle was measured by TIMS. The results show that the problem of particles losing is avoided in the process of sample preparing, particle locating and transferring. The bias from the certified value of CRM U 200 is less than 2%.