AbstractIn this study we pretreated Aramid yarns with ethylenediamine (EDA), diethylene triamine (DETA), and triethylene tetraamine (TETA) under different conditions to study some of their physical properties. The tensile strength retention, dye absorption (basic dye), and wicking height changed increasing pretreatment temperature, time period, and amines concentration. The glass‐transition temperature and the density of the crystals were ranked as follows: EDA > DETA > TETA; however, the degrees of the surface void were inverse. We concluded that the polymer chains of the Aramid fibers were rearranged through shrinkage of the pretreated Aramid fibers during pretreatment, and the hydrolysis of the Nomex polymer chains occurred under higher amine concentrations. The former phenomena were confirmed with differential scanning calorimetry, dynamic mechanical analysis, and X‐ray diffraction analyses, and the latter were confirmed with Fourier transform infrared spectroscopy and basic dye adsorption analysis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 70–76, 2005