The increasing contamination of water by organic dyes causes water pollution in the enviroment. Factories discharge untreated effluents into nearby water courses adding to the existing water pollution; this poses a significant environmental challenge. Hence there is a pressing demand to develop efficient technology for wastewater treatment, and photocatalysis has emerged as an advanced oxidation process with a green chemical approach for such treatment. This study aims to synthesize montmorillonite/TiO2 (Mnt/TiO2) photocatalysts and clarify the effect of montmorillonite content on the photodegradation of the organic dye rhodamine B (RhB). Mnt/TiO2 was prepared by a chemical method with various mass ratios of mMnt:mTiO2 based on the cation exchange capacity (CEC) of Mnt. The physicochemical properties of the samples prepared were determined by the following methods: energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The photocatalytic degradation efficiency of the RhB solution of Mnt/TiO2 was investigated by UV-Vis spectroscopy under UVC irradiation. Liquid chromatography-mass spectrometry (LCMS) was used to identify the photocatalytic by-products. The results showed that the structure of the nanocomposites has a ‘house-of-cards’ form with TiO2 nanoparticles randomly distributed on the surface and sheets of clay minerals. The best mass ratio of mMnt:mTiO2 is 10:1, corresponding to a 10 ppm RhB solution decolorization efficiency of 91.5% in 210 min. In this study, Mnt/TiO2 successfully cleaved the dye chromophore structure and broke the RhB rings into small and broken-ring compounds.