ABSTRACT Background and Objective Health impacts of inhaling airborne microplastics have been actively investigated. Although microplastics have been detected in lung tissues and bronchoalveolar lavage fluids, their detection requires substantial effort and is technically challenging, with existing studies demonstrating various limitations. Bronchoalveolar lavage fluid is a less invasive sampling method than surgical lung biopsy. This study aimed to establish a detection method for microplastics from bronchoalveolar lavage fluid and evaluate the relevant health impacts. Methods Patients undergoing bronchoscopy for diffuse lung disease diagnosis were included. Microplastics were detected using Nile Red staining and fluorescence microscopy. Particle size, shape, and concentration were assessed through image analysis, and plastic types were identified via Raman spectroscopy. Correlations between microplastic findings and clinical laboratory data were evaluated. Results Microplastics were detected in the bronchoalveolar lavage fluid of all 30 patients. The median concentration of Nile Red‐stained particles was 684.7 particles/mL, and over 80.0% of the particles were smaller than 10 μm, with 93.5% being particulate and 6.5% fibre. The most frequently identified microplastics were polyvinyl chloride, polystyrene, and polyethylene terephthalate. Microplastic concentration positively correlated with blood C‐reactive protein levels (r s = 0.39) and was higher in areas showing consolidation shadows ( p = 0.024). Conclusions We established a method for detecting microplastics in bronchoalveolar lavage fluid. Microplastics were found in all patients, with a potential link to inflammation. In addition, Nile Red staining was applied for the first time to detect plastics in the lung and appeared to be useful for screening and quantification. image