<p>Actinomycosis is a rare, chronic granulomatous infection caused by <i>Actinomyces</i> species, with urachal involvement being exceptionally uncommon. We report a rare case of urachal actinomycosis in a 29-year-old female presenting with a 6-month history of chronic pelvic pain. Contrast-enhanced computed tomography revealed a heterogeneously enhancing pelvic mass centered at the bladder dome, with apparent infiltration of adjacent structures and omental and serosal deposits, strongly suggestive of urachal carcinoma with peritoneal carcinomatosis. Laboratory tests, including tumor markers, were normal, and multiple image-guided biopsies were inconclusive. Diagnostic laparoscopy revealed no omental or peritoneal deposits, but a firm mass adherent to the bladder dome and surrounding tissues was identified. Histopathology demonstrated filamentous basophilic colonies with sulfur granules consistent with <i>Actinomyces</i> species, confirmed by Grocott’s methenamine silver and periodic acid–Schiff staining. The patient responded favorably to high-dose intravenous antibiotics followed by prolonged oral therapy. This case underscores urachal actinomycosis as a rare but important mimic of urachal carcinoma and highlights the indispensable role of histopathology in distinguishing infectious from malignant pelvic masses.</p>