The study aimed to analyze rainfall trend in Tonle Sap Lake regions of the Lower Mekong Basin and to determine if these time series belonged to a similar regime, have had any significant trends. To reveal the behaviors of annual and monthly rainfall for trends, historical data series of available 6 stations in more than 30 years from the 1980s to 2012 were used in this study. From the basic daily rainfall data, total and means of monthly and annual rainfall are formed for each individual station together with other basic statistics. These statistic results were used to investigate the spatial pattern of the inter-annual variability of annual rainfall totals over the study area. To detect the change, the annual rainfall data were subjected to process the intervention analysis (using Cumulative Summation technique) and step change analysis (using rank-sum test) and subsequently the trend in individual rainfall station were determined using Mann Kendall (MK) test. The applied methods presented similar results for annual rainfall trend. It emphasizes that the time-series of the annual rainfall variation in Tonle Sap Lake region presented no significant trend (statistically significant at p<0.05) for all stations. The result of the monthly trend shows the presence of increasing in the monthly rainfall amounts from January to May (mid of dry season to start of rainy season) in the investigated period.