Flesh and skin of red dragon fruits contain anthocyanins which are potential as a natural dye. This study aimed to improve the stability of anthocyanins using the copigmentation method. The stages on this study were maceration, extraction, evaporation, and copigmentation. The anthocyanins levels in the sample were determined by measuring the absorbance using UV-Vis spectroscopy. Copigmentation was carried out by adding anthocyanins with alum, Al2(SO4)3, in ratio of 1:1; 1:2; and 1: 3 by volume. Stability of the color was tested by storing of the solutions and the cotton fabrics at room temperature for 0, 3, and 6 days. The results analysis showed that the anthocyanin levels in flesh and skin of red dragon fruit were 13.20 mg/100 g and 5.37 mg/100 g. Stability of anthocyanin with copigment alum Al2(SO4)3 in a ratio of 1:1, 1:2, and 1:3 and a storage time of 0, 3, and 6 days of the cotton fabrics showed decreasing in color intensity due to the degradation and temperature. The color change in the copigmented extract to yellow compared to the pure anthocyanin