We experienced a rare case of the tuberculous arthritis of the right knee joint with a large popliteal cyst. The patient was 67 years old male suffering from right gonalgia since 7 years. Two years ago he became aware of the cyst at the popliteal region. With cystgraphy the cyst consisted of two parts was recognized. These were communicating with each other at th point of tibio-fibular joint and perforated into the joint. The cyst and the joint filled with tuberculous effusion. We considered that the origin of these cysts was the lateral gastrocnemius bursa and popliteus bursa. Histopathological study showed tuberculous-change in these cyst wall.