Hyaline ring granuloma (HRG) is a comparatively rare inflammatory condition occurring mainly in the oral region, and is characterized by hyaline rings (HRs) formed in the granulation tissue. This study describes a case of HRG occurring in the mandibular periosteum of an 18-year-old male. Histopathologic, histochemical and electron microscopic studies were performed on surgically excised materials. Histopathologically, ovoid bodies (OBs) surrounded by thin hyaline walls and HRs showing pale-stained eosinophilic thick hyaline walls were both detected. Histochemical study revealed that the OBs contained many granules chiefly composed of starch. Ultrastructurally, the HRs presented a stratiform structure due to the accumulation of cross-banded collagen fibrils with a basement membrane-like lining containing cellulose microfilaments. These results suggest that HRs are formed as follows: the exogenous vegetable materials are encapsulated by collagen, then the component is gradually degraded; the residual cellulose fraction adheres to the inner surface of the collagenous capsules, and the continuous deposition of collagen at the outer surface of the capsules increases its thickness. Finally, thick hyaline walls of HRs are formed. The possible pathogenesis of this curious lesion is discussed for stomatologists.