Microplastics have aroused global concern due to their widespread environmental distribution and the possible danger they pose to humans, animals, and microbes. In response to this concern, photocatalytic degradation, a technique that utilizes semiconductor nanomaterials as the photocatalyst, is being explored to reduce microplastics into less harmful compounds, making it a game-changing strategy for addressing this environmental problem. Besides the superiority of titanium dioxide (TiO2) as a photocatalyst, zinc oxide (ZnO) nanoparticles are also one of the semiconductors that have been widely explored to date. Studies have proven its potential to degrade microplastics in either solid- or aqueous phases. In the photocatalytic degradation of microplastics, the reactive oxygen species (ROS), including hydroxyl (•OH) and superoxide ions (O2•-), play an essential role in the process, resulting in the breakdown of the polymeric chain and the generation of reaction intermediates. Therein, the primary focus of this review is limited to the photocatalytic degradation of microplastics using a ZnO-based photocatalyst and its mechanisms. The exploration and comparison of microplastic’s solid- and aqueous-phase photocatalytic processes in terms of their experimental setup and performance were also discussed further. Furthermore, an insight into future research prospects is also suggested here, based on the restrictions of present photocatalytic degradation systems.