This report describes the morphological and immunohistochemical findings of a case of apparent collagenofibrotic glomerulonephropathy in a 7-month-old dog. Clinical examination showed moderate protenuria with elevated blood urea nitrogen and creatinine. Histopathological examination of the glomerular capillary walls and mesangial areas revealed diffuse and global accumulation of eosinophilic homogeneous or fine fibrous materials, which were immunohistochemically positive for type III collagen. On electron microscopy, the randomly crossed fibrils had transverse bands with a periodicity of approximately 60 nm. The clinical, histopathological, immunohistochemical and electron microscopic findings of the present dog were consistent with those of the human, childhood form of collagenofibrotic glomerulonephropathy.