The purpose of this study to find out the reasons behind infant mortality in South Asian countries. This problem depends on many factors. For finding the fact the study has gone through the reports of the database of World Bank and World Factbook. Using time series data (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014), the study explored the association between Infant Mortality Rate and Socio-Economic Determinants (birth attended by skill health staff, dependency ratio, literacy rate, mother's mean age at first birth, population growth rate and population below poverty level). Through the multiple regression analysis, the study found that out of various reasons, Birth attended by skill health staff (BASHS), Literacy rate (LR) and Population Growth Rate (PGR) have influence on Infant Mortality. In developed counties, governments ensure many facilities to prevent infant mortality whereas in developing countries, policies of government do not support. As a result, infant suffers much. The finding of the study may be useful for the policy makers that how infant mortality can be decreased.