Multi-layer graphene nanoplatelet (mGNP)/poly(methyl methacrylate) (PMMA) nanocomposite flexible thin films were prepared at various GNP loadings (1–5 wt%) and their optical properties were investigated in the UV, visible, and near IR region (200–850 nm). The transmittance and reflectance of the films reduced with an increase in the GNP loading. Although it is known that the transmittance of pure graphene is independent of wavelength, it was observed that in the UV region, the optical properties of mGNP/PMMA are wavelength-dependent. However, at higher GNP loadings (3–5%), these films have shown optical properties with less wavelength dependency. This may be attributed to diverse types of attenuation mechanisms in the nanocomposite films when graphene is incorporated as filler in the polymer matrix. In the visible region (400–700 nm), no such wavelength-dependent optical properties were observed. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.