Wetlands are among the most valuable and productive aquatic ecosystems and have many ecological and environmental functions, however they have been recently impacted by adverse climate conditions and numerous human interventions. The Shadegan international wetland and wildlife refuge is one of the largest wetlands of Iran which is located in the southwest of the country. In this study monthly changes of ecological indices (during 2003-2017) of the shadegan wetland including NDVI (Normalized Difference Vegetation Index), WST (Water Surface Temperature), MNDWI (Modified Normalized Water Index), LSWI (Land Surface Water Index), VWR (Vegetation-Water Ratio), MVWR (Modified Vegetation-Water Ratio) and Chlorophyll-a concentration (Chl-a) were investigated and monitored using MODIS images. The results showed a significant decreasing trend for time series of NDVI and MVWR where the Change Point Detection (CPD) for these indices were found at October 2011 and October 2012, respectively. Also, a significant increasing trend was observed in MNDWI and LSWI and the CPD for these indices were found at October 2012 and September 2012, respectively. The time series of WST and VWR showed no significant changes during the study period. In the case of Chl-a concentration due to data discontinuity, it was not possible to calculate the trend and other statistical criteria, however it seems that this index shows a decreasing trend. In order to investigate the potential critical transitions in the Shadegan wetland, the early warning signals such as first-order autocorrelation, standard deviation and skewness were also calculated and analyzed for each of the ecological indices. The results showed that the Shadegan wetland has experienced important ecological alterations mainly during 2009-2014, however only a sign of early warning of critical transition was detected in the autocorrelation criterion for NDVI. Keywords: The Shadegan Wetland, Ecological Indices, Remote Sensing, MODIS, Critical Transition.