The effect of Transglutaminase (TGase) on rupture strength of lactone tofu was studied by changing the content of Glucon-Delta-Lactone (GDL); the incubation temperature and the holding time; and the action mechanism was also discussed. The results showed that appropriate amount of TGase could obviously improve the gel strength of lactone Tofu. The optimum parameters were as follows: 0.3%GDL; 0.05% TGase; 3 h holding time and 50 ℃ holding temperature. The results of SDS-PAGE showed that the α′ and α subunits in 7S and the A3 peptide in 11S were most closely related to TGase; followed by the β and γ subunits in 7S and the A peptide in 11S.