CdxCu1-xS and ZnxCu1-xS (x=0.5; 0.25 and 0.75) nanocrystals have been synthesized into functional nitrile butadiene rubber (FNBR) matrix. The structural and optical properties of obtained nanocomposites are investigated by X-ray diffractometer (XRD) and UV–visible spectroscopy. The effects of SILAR cycles and Cd(Zn)/Cu ratio on the formation of the crystals and their band gap has been studied in detail. The photocatalytic efficiency of FNBR based ternary nanocomposites of CuCd and CuZn sulfides were estimated towards the photodegradation of Malachite green dye under visible light irradiation. The average crystallite size and band gap of the obtained CdCuS and ZnCuS nanoparticles were calculated via Scherrer and Tauc equations, respectively. The Tauc equation from the absorbance data for Cd0.5Cu0.5S/FNBR and Zn0.5Cu0.5S/FNBR nanoparticles are ~3.64 eV and ~3 eV, respectively. Cd0.5Cu0.5S/FNBR and Zn0.5Cu0.5S/FNBR nanocomposites show 2 or 4 band gap values on the same Tauc plot. As seen in XRD, mixed crystal phases and defects also occurred on the ternary sulfide formation. Photodegradation of cationic dye shows that ternary metal sulfide nanocomposites are very good photocatalyst under visible light irradiation.