Abstract: Using the climatological data and aerological reports of the years 7951-1957, the author investigates the characteristics of Climate of May-Yü in Far East and its relation to the behaviour of circulation over Asia. It is found that May-Yü occurs in the transitional period from spring to summer. The onset of May-Yu is associated with the outburst of Indian Monsoon. They are closely related with the dissolution of the jet stream to the south of Himalaya. When the jet stream over Japan disappears and easterly wind begins to appear, the May-Yü period terminates. The change takes place in the same manner each year. The results are helpful to prediction.