A well-preserved late Warring States period tomb unearthed in Yiyuan, Shandong Province contained a great number of burial accessories. Among these burial accessories were found leather objects. The discovery of archaeological leather is rare in archaeological excavations in the North of China. Those objects are important for the study of ancient northern region leather tanning procedures. The archaeological leather samples were studied by using the attenuated total reflection Fourier transform infrared spectroscopy (ATN-FTIR) and scanning electron microscope (SEM) to obtain insight into the functional groups and pattern of collagen fibrils of the waterlogged Warring States period leather. For comparison, modern sheep leather samples were analyzed using the same approach. The ATR-FTIR comparisons of the archaeological leather and modern leather showed that the archaeological leather contained the characteristic absorption bands of the leather. The SEM studies indicated that the pattern of collagen fibrils of the waterlogged leather was similar to that of modern sheep leather. This study provides a reference for identification of the archaeological leather.