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Mesoscale convective systems (MCSs) are important precipitation‐bearing phenomena in the Tropics. Hence, it is important to elucidate the temporal variation of MCSs. This study investigated the interannual variation of MCSs in Bangladesh and surrounding area during June–September using 3‐hr TRMM3B42 precipitation data. After objective detection of propagating MCSs (PMCSs), their statistical features were analyzed. It was found that the annual number of PMCSs decreased significantly during 1998–2015. The most remarkable decrease was in southward PMCSs generated over land, consistent with the observed decrease in precipitation. Recent weakening of the low‐level southwesterly and stabilization of the atmosphere probably contributed to the decrease of PMCSs. Because southward PMCSs generated over land were present on about 40% of days with heavy rain, PMCSs clearly have a crucial role in precipitation variability. The findings of this study suggest that investigation of MCSs is essential for understanding precipitation response to climate change in South Asia. Interannual variations of mesoscale convective systems (MCSs) over South Asia were analyzed over 18 years (1998–2015). Significant decrease in number of MCSs was detected in association with weakening of low‐level southwesterly during summer monsoon. The MCSs largely contribute to precipitation, and therefore, it is suggested that MCSs influence the uncertainty in future precipitation change. [ABSTRACT FROM AUTHOR]