The betacyanin pattern of Djulis (Chenopodium fromosanum), a native cereal plant in Taiwan, was reported for the first time. The determination of characteristics of the pigment, including pH and thermal stability and their relation to antioxidant activities, indicated that betacyanin of Djulis exhibited the maximum absorbance at 530 nm and their thermal stability was dependent on the pH. Antioxidant capacities as well as red color of that pigment were significantly positively related with A(530). Therefore, A(530) can be used as a simple index of the antioxidant capacity of that pigment. Four peaks including betanin (47.8%), isobetanin (30.0%) with m/z 551.0, and armaranthin (13.6%), isoamaranthinee (8.6%) with m/z 727.0 were purified from the pigment extract by HPLC and identified through LC/MS. Among them, betanin and isobetanin totally accounted for more than 70% of FRAP reducing power or DPPH scavenging capacity and were a major source of the antioxidant capacities. Our findings of this pigment confirmed that Djulis can be used as a novel source of betanin antioxidants and may provide a basis for its sustainable utilization in the food industry.