Giant left atrial diverticulum is a rare congenital malformation that is most commonly diagnosed in incidental finding. Here, we reported a case of a 1-year-old asymptomatic child with a giant left atrial diverticulum. Diagnosis was established by transthoracic echocardiography (TTE), and confirmed by multidetector computed tomography (MDCT) and transesophageal echocardiography (TEE). We excised the diverticulum and sewed its base under cardiopulmonary bypass and cardiac arrest. The patient had a good postoperative result.