In the field of stormwater management, multiple studies have been conducted on bioretention efficiency in removing common stormwater pollutants (e.g., oil and grease, heavy metals, and nutrients.) However, its application in removing microplastics is still in preliminary stages. This study aims to fill a clear knowledge gap regarding the removal efficiency of microplastic particles in bioretention soil media. Laboratory experiments were designed to evaluate and analyze the effects of bioretention media characteristics with various stormwater parameters on microplastic removal efficiency using fluorescent microscopy to detect particles after simulated storm events. The study examined three unique sizes and types of microplastic particles. Changes in removal efficiency were largest when comparing different sizes of particles. Average removal efficiency for 33.1 μm polystyrene measured 98.45% while average removal efficiency for 3.93 μm polystyrene measured 68.71%. Microplastics of similar size but different type showed comparable results as 22-27 μm polyethylene measured 95.47%. The 33.1 μm polystyrene microspheres were also tested in the presence of two common stormwater co-contaminants. The presence of heavy metals reduced the average removal efficiency to 86.26%. The presence of motor oil with 33.1 μm polystyrene yielded a comparable average removal efficiency over the total duration of the simulated event, but showed a reduction in removal efficiency with time.