A 68-year-old man, who had no remarkable past medical history, was referred to a hospital because of disorientation and right-sided hemiparesis. On magnetic resonance imaging, a contrast-enhanced tumor in the left frontal lobe with perifocal edema was noted. He underwent left frontal lobectomy. Microscopic examination revealed infiltrative atypical astrocytes showing increased cellularity, distinct nuclear atypia, and many mitotic figures, while microvascular proliferation and necrosis were absent. Thus, the tumor was histologically diagnosed as anaplastic astrocytoma. It was of note that cytoplasmic eosinophilic granules were observed in approximately 25% of neoplastic cells. The granules were positively immunostained with anti-alphaB-crystallin antibody, and the other histochemical and immunohistochemical results also corresponded to Rosenthal fibers. The MIB-1 labeling index of the highest area of the tumor was 22%, while that of granular cells was 2.1%. An ultrastructural study revealed amorphous electron-dense structures attached to intermediate filament bundles, compatible with Rosenthal fibers. Such structures are relatively common in oligodendroglial tumors; however, they are extremely rare in astrocytic tumors. Fluorescence in situ hybridization targeted against chromosome 1 failed to demonstrate allelic loss of the short arm. The present case should also be discriminated from granular cell astrocytoma. We review related literature and discuss the significance of granules in gliomas.