Abstract: Anthocyanidin synthase (ANS) is one of the key enzymesthat catalyzes the biosynthesis that converts leucoanthocyanidin into colored anthocyanidin in plants. To study the diversity and origin of ANS, the ANS genes from 7 varieties of Hanzhong Black Rice were analyzed by PCR cloning and sequencing. Through the bioinformatics, sequences of theANS genes were compared. By constructing the NJ and homology trees, the sequence alignment of ANS protein, basic physical and chemical properties, subcellular localization, transmembrane region, signal peptide, guide peptideas well as the secondary and tertiary structures of ANS protein were studied. The results showed that the ANS genes of theserice varietiescould be divided into two categories, namely, Black Rice 1(BR1) and Black Rice 2(BR2). They had a same length on the open reading frame of 1, 128 bp encoded 375 amino acids. Their phylogenetic treessuggested that BR1 and BR2 were genetically close to other gramineous plants, such as Indica and Japonica, Indosasa hispida, and Triticum aestivum. The sequence of amino acids (AA) revealed that only the 326^th AA was different between BR1 and BR2. A conserved domain search showed that the ANS protein hada 2OG-FeⅡ_Oxy domain. Its predicted tertiary structure indicated that BR1 differed from Indica, and suggested that the ANS gene might play a key role in the anthocyanin synthase. It was concluded that the ANS genewas ancient and could be served as a reference gene for species identification, and thatits presence in Hanzhong Black Rice could be one of the main reasons why the anthocyanin synthesis was found in the rice.