Archaeological waterlogged leathers dated from the 13th to 17th century have been analyzed using carbon-13 high-resolution solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). The NMR and EPR spectra have been compared to modern vegetable-tanned leathers and crude hide. Both techniques allowed us to fully characterize the samples and better understand the changes occurring during aging in water environment. The main features of the archaeological leathers are the high contents in iron and the absence of residual vegetable tannins. Traces of lubricants could not be detected either. The accumulation of iron oxides may have played a role in the conservation of the archaeological objects and explain the surprising good conservation state of the leather samples as was observed in the NMR spectra. The absence of tannins and lubricants in the studied archaeological samples is also discussed. It may be a consequence of aging in water-rich environment. The analysis strategy described in this paper can be systematically applied to characterize archaeological or historical leather samples.