A case of malacoplakia of the prostatic gland associated with prostatic nodular hyperplasia from a 69 years old man was presented, and its light and electron microscopic and immunohistochemical features were discussed along with its pathogenesis. This lesion was incidentally found in a transurethral prostatectomy specimen, and consisted of large number of epithelioid cells in which were typical cytoplasmic inclusions known as Michaelis-Gutmann bodies. Ultrastructurally, these inclusions showed a dense, central calcified bodies of various developmental stages. Immunohistochemical study using antilysosomal antibody revealed no lysosomal activity. Based on these findings, we could suspect that main problem for this development of malacoplakia is altered intracellular digestion process of foreign biologic materials.