The triethylenetetramine (TETTA) surface-modification process for fibers, consisting of short-time annealing and high-temperature treating the fibers previously padded in TETTA, has been developed. The annealing (60 s, 170 degrees C) of the fibers was performed to restrict the reaction on the surface. To characterize the structure and properties of TETTA-modified fibers, IR spectroscopy, DSC, and X-ray diffraction were applied and critical dissolution time, dye uptake, density, and basic physical-mechanical properties were determined. It was shown that after annealing and aminolysis of the fibers T-g increases to 115 degrees C, while the crystallinity index (determined by DSC) is changed from 33 to 46% (X-ray crystallinity increased from 47 to 59%) and critical dissolution time increased from 12.9 to 58.9 min, depending on the time of aminolysis. The results obtained suggested the existence of two simultaneous processes during the aminolysis : macromolecular scission responsible for introducing the amine groups at the surface and partial crystallization of PET.