Plastics are used commonly in the world because of their convenience and cost effectiveness. Microplastics, an environmental threat and human health risk, are widely detected in food and consequently ingested. However, degraded plastics are found everywhere, creating an environmental threat and human health risk. Therefore, real-time monitoring of orally administered microplastics to trace them in the body is tremendously important. Methods: In this study, to visualize their absorption path, we labeled polystyrene with [64Cu]Cu-DOTA. We prepared radiolabeled polystyrene with 64Cu. Afterward, [64Cu]Cu-DOTA-polystyrene was orally administered to mice, and we evaluated its transit and absorption using PET imaging. The absorption path and distribution of [64Cu]Cu-DOTA-polystyrene were determined using PET over 48 h. Ex vivo tissue radio-thin-layer chromatography (TLC) was used to demonstrate the existence of [64Cu]Cu-DOTA-polystyrene in tissue. Results: PET images demonstrated that [64Cu]Cu-DOTA-polystyrene began to transit to the intestine within 1 h. Accumulation of [64Cu]Cu-DOTA-polystyrene in the liver was also observed. The biodistribution of [64Cu]Cu-DOTA-polystyrene confirmed the distribution of [64Cu]Cu-DOTA-polystyrene observed on the PET images. Ex vivo radio-TLC demonstrated that the detected γ-rays originated from [64Cu]Cu-DOTA-polystyrene. Conclusion: This study provided PET evidence of the existence and accumulation of microplastics in tissue and cross-confirmed the PET findings by ex vivo radio-TLC. This information may be used as the basis for future studies on the toxicity of microplastics.