This paper has analysed the characteristics of low frequency oscillation of cloudiness in the tropical area (90°E-170°W.) during the period of May 1978-Dec. 1984, using GMS 5-day mean cloudiness data. The main results are:1. There are two kinds of oscillation in the Indian ocean and western Pacific oceans. One is the 30 to 60 day mode. The other kind, is in a cycle of 2 to 4 years, named very low-frequency oscillation.2.During the non-El .Nifio years, the 30 to 60 day mode is more clear. But.its propagation is depressed during the El Nino year. .3.The 2 to 4 years mode is mainly associated with the El Nino phenomenon.