Archaeological leather has been buried in a wet, anoxic environment for an extensive period of time, which has resulted in the degradation of its tannins. This process, in addition to the removal of lipids, has caused damage to the leather’s structure, primarily due to the deterioration of collagen, which is the leather’s primary component. In the present work, after artificial aging by soaking in acid solution, the waterlogged leather was characterized in terms of hydrothermal stability, morphology and structure by shrinkage temperature indicator, optical super depth-of-field microscope (OSM), high-precision color difference instrument, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results showed that the vegetable-tanned leather was deteriorated with color change and decrease in hydrothermal shrinkage temperature (Ts) and pH, after the artificial aging treatment. The changes in the structure of the samples were analyzed from the amide I band of collagen analyzed by deconvolution of the infrared spectra, which indicated that the content in the random structure in collagen is increased by artificial aging.