Abstract: By using the object MJO index and def i ning the clustering of tropical cyclone (TC) activities over the Western North Pacific (WNP), the clustering characteristics of tropical cyclones and their associations with MJO are discussed. The results show that 1) the frequency of the clustering of TCs is 3.6 per year in the south of 30°N over the WNP. There was a decreasing trend of the frequency of the clustering TC activities during 1978 to 2009, while there was not any trend of the intensity. 2) The clustering of TC activities favor occurring in MJO phase 5 and 7, when the strong MJO convection locates in the east of Indonesia and the east of western Pacific, while they seldom occur in MJO phase 1 and 2, when the strong MJO convection locates in Africa and the west of Indian Ocean.3) The characteristics of MJO propagation change after the clustering TC activities, such changes may possibly be related to the cluster activities themselves and the changes of the air-sea variables which they have brought about.