Detection of reticuloendothelial system (RES) cells is essential for the differential diagnosis of splenic hamartoma. Among the imaging techniques using contrast agents phagocytosed by RES cells, contrast-enhanced ultrasonography (CEUS) with Sonazoid is less invasive and less costly than Tc-99m-labeled colloid scintigraphy. We report a case of non-symptomatic splenic hamartoma in a 40-year-old woman detected as an abdominal tumor by screening ultrasonography. The tumor was 4 cm in diameter, round, slightly hypoechoic, and associated with a cystic lesion. The tumor region was stained on enhanced computed tomography with prolonged enhancement, while the cystic lesion was not. The mass appeared as mainly isointense with partial hyperintensity on T1-weighted and as a mixed hypo- and hyperintense region on T2-weighted magnetic resonance images. Tc-99m-labeled colloid scintigraphy demonstrated uptake in only the tumor region. CEUS with Sonazoid revealed that the tumor was mainly hypervascular with non-enhanced areas in the early vascular phase, but the hypervascular region appeared also as a hyperechoic area (indicating microbubble phagocytosis) in the post-vascular phase. Thus, CEUS with Sonazoid revealed all three cardinal features of splenic hamartoma: hypervascularity, presence of RES cells, and tissue heterogeneity. Splenectomy and histopathology confirmed the presence of a splenic hamartoma with associated hematoma. CEUS with Sonazoid is a promising new diagnostic tool for splenic hamartoma.