Due to the wide presence of microplastics in water, the interaction between microplastic particles and microalgae cells in medium merits the attention of researchers. Microplastic particles can impact the original transmission of light radiation in water bodies since the refractive index of microplastics is different from that of water bodies. Accordingly, the accumulation of microplastics in water bodies will certainly impact microalgal photosynthesis. Therefore, experimental measurements and theoretical studies characterizing the radiative properties of the interaction between light and microplastic particles are highly significant. The extinction and absorption coefficient/cross-section of polyethylene terephthalate and polypropylene were experimentally measured using transmission and integrating methods in the spectral range of 200–1,100 nm. The absorption cross-section of PET shows remarkable absorption peaks in the vicinity of 326 nm, 700 nm, 711 nm, 767 nm, 823 nm, 913 nm, and 1,046 nm. The absorption cross-section of PP has distinctive absorption peaks near 334 nm, 703 nm, and 1,016 nm. The measured scattering albedo of the microplastic particles is above 0.7, indicating that both microplastics are scattering dominant media. Based on the results of this work, an in-depth understanding of the interaction between microalgal photosynthesis and microplastic particles in the medium will be obtained.