The native polymorphic structures of chitin, namely alpha- and beta-chitin, were studied with X-ray diffraction (XRD), infrared and Raman spectroscopies, and sum-frequency generation (SFG) vibrational spectroscopy. The currently proposed model of alpha-chitin crystal based on X-ray and electron diffraction study has an antiparallel chain arrangement imposed by the orthorhombic symmetry in contrast to parallel chain arrangements in beta-chitin and native cellulose; however, the natural occurrence of antiparallel chain arrangement for alpha-chitin is controversial to widely accepted biosynthetic mechanisms for structural polysaccharides such as chitin and cellulose, where chains are successively polymerized and crystallized in a unidirectional way. We compared the SFG signals among samples with similar crystallinity, morphology, and textures but differing in allomorphs. The SFG signal from alpha-chitin was similar to 40-fold weaker compared to beta-chitin having a similar lateral dimension. The strong SFG signals arising from beta-chitin can be explained by a net polar ordering of parallel packed chains. These results strongly supports the antiparallel chain orientation and high symmetry (orthorhombic) of alpha-chitin suggested by diffraction analysis.