Microplastics (MPs) pollution has become a major environmental problem and poses a risk to a variety of organisms. In this study, the photoaging behavior of acrylonitrile butadiene styrene microplastics (ABS-MP) in aqueous environment was investigated under simulated solar irradiation. Results showed that the long chains of ABS-MP broke under the light irradiation, and its thermal stability was reduced. ABS-MP was oxidized during photoaging and produced a large number of oxygen-containing functional groups. Structure destruction of ABS-MP decreased the formation of environmentally persistent free radicals (EPFRs) and further photoirradiation generated secondary EPFRs. Nuclear magnetic resonance (NMR) analysis of the aged leachates confirmed that ABS-MP was oxidized and some small molecular fragments were dropped during photoaging. Meanwhile, C-Br bond broke of additive tetrabromobisphenol A (TBBPA) resulting in more bromine released into water and Sb(III) of additive Sb2O3 was oxidized to Sb(V) during photoaging. These findings illustrate the necessity of considering the aging of MPs in natural environment, expand the understanding of the potential harm and fate of MPs in aqueous environment, which is important for the management of MPs.