Herein, we describe cases of pulmonary acute graft-versus-host disease (aGVHD) in two patients occurring after allogeneic hematopoietic stem cell transplantation (HSCT) due to precursor B-cell acute lymphoblastic leukemia in a 6-year-old patient and in acute myeloid leukemia in a 14-year-old boy. In both cases, chest CT revealed confluent ground-glass attenuation along the bronchovascular bundles, as well as some bronchial dilatation. Microscopically, in both cases we noted a characteristic bronchiolocentric pattern and bronchiolar epithelial changes, which included denudation of the bronchiolar epithelium, regenerating atypical cells, and wall thickening with subepithelial or transmural fibroblast proliferation, along with some lymphocytic infiltration. One patient died on day 86 after allogeneic HSCT due to sudden acute respiratory distress syndrome, and the other patient currently remains alive without active aGVHD. The authors' experiences in these two cases demonstrate that intense awareness of the pathologic findings of GVHD is mandatory after allogeneic HSCT.