Sand, an important constituent of concrete, has growing demand worldwide. Sand mining is the process of removal of sand particles from the natural eco system. In Tamil Nadu, 60 percent of the sand requirement is met by the quarries in Cauvery river basin. River sand mining can cause damages to both eco system and the livelihood of the people. Through literature, it was observed that the farmers in the riverine area are facing serious water shortage problems due to mining activities. As a result, the share of agriculture income to the farm households has been decreasing. Hence, an attempt has been made to analyze the effect of sand mining on farm income in lower Cauvery river basin of Tamil Nadu using decomposition analysis. The income differences were analyzed for two time periods 2010-11... and 2017-18 for the major crops in study area viz., Paddy and Banana. The analysis resulted that the contribution of sand mining in the income differences was at higher level in paddy and banana (46.56 and 26.60 percent respectively) in the study area.