In this study, nanocomposite was successfully synthesized using biopolymer material such as sodium alginate and carboxymethyl cellulose (CMC) by crosslinking using barium ion and modified by ZnO nanoparticles. Alginate/CMC/ZnO nanocomposites were characterized using using fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The measurement of the degradation solution was carried out using UV-Vis analysis and determined by the calibration curve of Congo red dye. The optimum condition of the photocatalytic reaction was obtained by using the weight of 60 mg nanocomposite, at pH of the solution at pH 3, ratio of alginate-CMC: ZnO is 1:0.8 reaction time of 110 min. Alginate/CMC/ZnO nanocomposite exhibited an excellent photocatalytic activity under sunlight irradiation with degradation percentage of 90.12 %. Reusability test on the use of alginate/CMC/ZnO nanocomposite was done 3 times. The Biopolymer-based nanocomposite of alginate, CMC, and modified by ZnO can be applied to reduce dyestuff biodegradable, it is economically viable and environmentally friendly.