In the present study, efficiency of a new magnetic nanocomposite (CoFe2O4@CuS) for photocatalytic degradation of PG in aqueous solutions was investigated. Structural characteristics of synthesized magnetic nano particles were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), Thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. Also, the effect of important parameters such as pH (3-11), nanoparticle dosage (0.1-0.8 g/L), PG concentration (10-100 mg/L) and contact time (10-120 min) were investigated. Results of FT-IR, XRD, EDX and Raman analyses showed successful synthesis of CoFe2O4@CuS magnetic nanocomposite. SEM and TEM images showed that the size of CoFe2O4@CuS magnetic nanocomposite was below 100 nm. Also, results of VSM analyses showed that CoFe2O4@CuS magnetic nanocomposite still has magnetic properties (Ms = 7.76 emu/g). According to the results of study, in photocatalytic degradation process of PG by CoFe2O4@CuS magnetic nanocomposite by UV light and in optimum condition (pH = 5, nanocomposite dose: 0.2 g/L, PG concentration: 10 mg/L and contact time: 120 min), maximum degradation of PG was 70.7%. Also the photocatalytic reaction almost followed the pseudo-first order kinetics. In addition, after five consecutive runs, the catalyst efficiency wasn't reduced significantly.