In this study, we report a novel PtSe2/graphene nanocomposite by facile ultrasonic-assisted techniques. The "as-prepared" nanocomposites were further characterized by various techniques such as X-ray diffraction, scanning electron microscopy with an energy dispersive X-ray analysis, transmission electron microscopy, UV-Vis absorbance spectra analysis, diffuse reflectance analysis, and Raman spectroscopic analysis. The photocatalytic activities of the composites were investigated by the degradation of rhudamine B and methylene blue as a standard dyes. The photodegradation rates of organic dyes by the nanocomposites are found to be markedly high. This study suggests that the as-prepared PtSe2/graphene composite can be utilized as highly efficient photocatalyst materials that employed visible light as an energy source.