<p>This study aimed to investigate the presence of microplastics in the gastrointestinal tract and lungs of white-eared opossums (<i>Didelphis albiventris</i>), as well as their effects on these organs and the body condition of sampled animals. We captured 22 opossums from April to December 2023 in six forest fragments of Campo Grande, capital of Mato Grosso do Sul state. Body condition estimates were performed using measurements of weight and head-body length for a total of 22 male and female opossums. Stomach, ileum, and lung fragments were collected during necropsies for histopathological study and detection of microplastics by alkaline digestion with KOH. Digested samples were vacuum filtered using filter paper and dried in an oven. The dried filters were examined under an optical microscope. A total of 270 microplastic specimens were detected in the 22 animals examined. The ileum presented the highest number of microplastics (<i>n</i> = 141), fibers were the most common type (<i>n</i> = 185), and blue was the predominant color (<i>n</i> = 140). Regarding chemical composition, the most frequently detected microplastics were polyvinyl chloride, polyethylene terephthalate, and acrylonitrile butadiene styrene. Although all <i>D. albiventris</i> specimens presented microplastics in their evaluated tissues, no effects on body condition or tissue damage were observed. Since <i>D. albiventris</i> are common animals in Campo Grande and are contaminated by microplastics, these animals can act as sentinels of environmental conditions.</p>