Anthocyanins are pigments belonging to the flavonoids group, widely used in food, cosmetics and pharmaceuticals; It has the ability to decrease oxidative stress. Aqueous biphasic systems (ABSs) are a promising and environmentally safe alternative (depending on the substances used) for the extraction of anthocyanins. This study aimed to extract anthocyanins from açaí through ABS and analyzed the effect of the length of the tie-line (LTL) on the partition coefficient of anthocyanins (K). The ABS used was formed by polymer solution of PEG1500 and saline solution of (NH4)2SO4. Phase diagrams of the ternary systems were determined using the turbidimetric titration method and the tie-lines were quantified using the gravimetric method. Othmer-Tobias correlation confirms the quality of the experimental LLE data (R2> 0.99). The NRTL and UNIQUAC models were used to correlate LLE data, with results of root-mean- square deviations (RMSD) of each model at 0.33 and 0.15%, respectively. After forming the blank system, the water composition of the four tie-lines was replaced by solution of citric acid at 25% to avoid anthocyanins degradation. The concentration of total anthocyanins was determined by pH-differential method. From the line with highest concentration of anthocyanins was realized a study of stability with duration of 5, 30, 60, 120, 240 and 360 minutes. It was observed that K is dependent of LTL, so that higher LTL result greater the value of K. The best extraction time was 5 minutes, where the upper and lower phase extracted 121.83 and 2.79 mg/100g of anthocyanins, respectively. Similar value was found for extraction with HCl in 5 minutes, resulting in 132.8 mg/100g of anthocyanins. The most efficient line presented a K value of 43.7 and the values of extraction via ABS were similar with the acid extraction, being verified that the system is promising for extraction of anthocyanins in ABS.