When microplastics (MPs) introduce into groundwater, they are likely to cause human health effects not only by the particles themselves, but also by the leaching of additives. Also, photo weathering occurring on the surface soil can change the leaching characteristics of additives in MPs, hence it is essential to quantitatively understand this effect. In this respect, the leaching behavior of di(2-ethylhexyl)phthalate (DEHP) from polyvinyl chloride (PVC) MPs was assessed according to the photo weathering in this study. PVC MPs were prepared as fragments at 125 μm or less, and exposed to UVC (254 nm) for different durations: 0 h (virgin), 360 h, and 600 h. The surface characteristics of the weathered PVC MPs were analyzed using Fourier transform infrared (FT-IR) (carbonyl index; CI), X-ray photoelectron spectroscopy (XPS) (O/C ratio), and a contact angle analyzer. The CI increased from 1.63 to 2.19, the O/C ratio increased from 0.14 to 0.24, and the contact angle decreased from 72.4° to 32.3° for virgin MPs and 600 h-weathered MPs, respectively. These results indicated an increase in oxygen-containing functional groups and a decrease in the hydrophobicity of PVC MPs owing to photoaging. Leaching experiments were conducted with artificial groundwater for 48 h to assess the leaching characteristics of DEHP from PVC MPs according to the UVC irradiation. The leached DEHP from virgin PVC MPs was 0.001% (w/w) after 48 h, and it increased to 0.002% for 360 h-weathered MPs, and 0.003% for 600 h-weathered MPs. This study demonstrated that the leaching of DEHP from PVC MPs into groundwater was facilitated through photo weathering of MP surface.