We reported herein the damp-heat aging of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate (VAc) consents simultaneously for weeks. The aging was carried out under temperature of 40 degrees C and relative humidity of 93% in air atmosphere. The changes of copolymers' Structures and properties were investigated by means of FTIR, wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) and mechanical tests. Cl values derived from ATR-FTIR spectra have a decrease when aging time is 1 week and then increase during damp-heat aging process which suggests the first loss then incorporation of O=C group. WAXD infer that the narrowing trend of FWHM and increase of crystal sizes may attribute to the melting and re-crystallization of secondary crystallization, which is also confirmed by DSC results. Mechanical tests including Shore A and Shore D hardness, modulus at 100%, tensile strength and elongation at break, are all depending on the primary crystallization and influenced little by damp-heat aging. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2358-2365, 2009