The present study investigates the interdecadal and interannual variations of Sri Lankan precipitation during Southwest Monsoon (SWM) and their connections with the Indian Ocean Sea Surface Temperature (SST) over 38 years (1979-2016).Empirical orthogonal function (EOF) analysis is applied to examine the spatial-temporal variations of precipitation in Sri Lanka and surrounding region.The first two leading EOF modes explain exceeding 70% of the total variance.EOF1 shows a monotonous mode.Both PC1 and 7-yr running mean of precipitation in Sri Lanka show clear interdecadal variations with more and less precipitation before and after 2000.The interdecadal variation of precipitation is associated with the warmer SST in the western and central tropical Indian Ocean during 2000-2014,which induces the anomalous downward motion over Sri Lanka through enhancing the meridional circulation,and thus depresses the precipitation over there.For EOF2 mode,negative signals are in most regions of Sri Lanka except in cape of northern Sri Lanka with positive signals.PC2 shows an interannual variation,and is significantly positively related to the SST anomalies in the southeast Indian Ocean.These warm SST anomalies could induce anomalous cyclonic circulation in the north tropical Indian Ocean due to Gill response,which is favourable for convergences of moisture flux and more precipitation in Sri Lanka.This study suggests that the interdecadal variation of precipitation in Sri Lanka is greatly associated with western and central tropical Indian Ocean SST,while the interannual variation is significantly influenced by the anomalous SST in the southeast tropical Indian Ocean.