Popliteal artery (PA) entrapment syndrome is a rare cause of popliteal artery aneurysm (PAA). Therefore, accurate diagnosis and definitive surgical management are required. We encountered a case of a middle-aged woman with a large pseudo aneurysm due to symptomatic anatomic entrapment. A 48-year-old woman with right leg edema and fatigue was referred to our department. Contrast-enhanced computed tomography revealed a 31 mm-diameter right PAA with a saccular shape resulting from type II entrapment syndrome. The right PAA compressed the right popliteal vein, causing right leg edema. Thus, elective surgery was scheduled. The patient was placed in the prone position, and a posterior approach with an L-shaped incision was performed. The PA was compressed by the medial gastrocnemius muscle arising from an abnormal lateral position. PAA originates in the distal part of the compressed lesion. The medial gastrocnemius muscle was divided. The PAA was resected and replaced with a saphenous vein graft from the left thigh. The postoperative course was uneventful, and the patient was discharged with satisfactory symptom reliefs. PA entrapment syndrome should be considered before treating PAA, especially atypical pseudoaneurysm without significant atherosclerosis.