The pathophysiological mechanisms underlying diabetic lung disease (DLD) remain poorly understood. Beyond hyperglycemia, dysregulated molecules such as adenosine may contribute to pulmonary inflammation and fibrosis. MRS1754, a selective antagonist of the A2B adenosine receptor (A2BAR), has demonstrated anti-inflammatory and antifibrotic effects, including reductions in macrophage (MΦ) infiltration in animal models of diabetes-associated complications; however, its effects on DLD remain unexplored. Here, diabetic Sprague-Dawley rats were treated with MRS1754, and pulmonary inflammation, fibrosis, MΦ infiltration, and polarization were assessed in bronchoalveolar lavage fluid (BALF) and lung tissue using immunohistopathological and molecular approaches. According to data normality, one-way ANOVA/Tukey’s test or Kruskal–Wallis/Dunn’s test were employed, as appropriate; ordinal data were analyzed using the Mann–Whitney test with Bonferroni correction. Compared with controls, diabetic rats exhibited pulmonary inflammation and fibrosis, increased MΦ infiltration, and an M1/M2 polarization imbalance. MRS1754 attenuated these alterations, reducing Tumor necrosis factor-alpha (TNF-α) and Transforming growth factor-beta 1 (TGF-β1) levels, decreasing MΦ accumulation in BALF and lung tissue, and fully restoring the M1/M2 balance to control levels. BALF MΦ populations, particularly the M2 (Cluster of differentiation 163-positive; CD163⁺) subset, correlated strongly with TGF-β1 and fibronectin (FN1) levels. Reanalysis of human fibrotic lung single-cell transcriptomic data further identified MΦ as a major TGF-β1-expressing cell population. Collectively, these findings suggest that A2BAR antagonism partially mitigates inflammation, fibrosis, and MΦ infiltration while fully restoring MΦ polarization balance in DLD, supporting its potential as a therapeutic strategy.