Primary small cell carcinoma of the prostate is extremely rare. Herein reported is a case of primary small cell carcinoma of the prostate with immunohistochemical examination of KIT and platelet-derived growth factor-α. The present case is unique in that the small cell carcinoma did not express neuroendocrine antigens. A 68-year-old man was found to have high serum prostate-specific antigen, and biopsy showed malignant small tumor cells fulfilling the small cell carcinoma criteria of the World Health Organization. Immunohistochemically, tumor cells were positive for pan-cytokeratin, KIT, platelet-derived growth factor-α, p53, Ki-67 labeling = 65%, prostate-specific antigen and alpha-methylacyl-CoA racemase. Tumor cells were negative for vimentin, CD56, synaptophysin, chromogranin and neuron-specific enolase. Imaging modalities showed multiple metastases, and the patient was treated by chemotherapy. The present report is the fifth with immunohistochemistry of prostatic small cell carcinoma.