We have investigated the effects of Cr3+ on the hierarchical structure of pigskin collagen fibers by use of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffraction (WAXD), confocal laser micro-Raman spectroscopy (CLRS), and circular dichroism (CD). Our results demonstrate that the introduction of Cr3+ leads to the formation of a cluster of 20-40 nm between collagen fibrils, while the unique axial periodic structure (D periodicity) of the fibrils does not change. As the Cr3+ concentration increases, the order of intermolecular lateral packing, crystallite structure within helical chains, and N and C telopeptide regions decrease. The present study reveals that Cr3+ only cross-links with collagen but does not disrupt its triple helical structure.