OBJECTIVE: To evaluate the relationship between serum neutrophil-to-lymphocyte ratio (NLR) and severity of meconium aspiration syndrome (MAS). METHODS: We retrospectively analyzed 197 neonates who admitted for MAS between 2008 and 2016 at the neonatal intensive care unit of Dong-A University Hospital. The serial changes of NLR were analyzed from 1st to 3rd day of life. The NLR was compared by disease severities (non-invasive respiratory care group vs. invasive respiratory care group and MAS with or without persistent pulmonary hypertension of the newborn [PPHN]). RESULTS: The NLR values from 1st to 3rd day of life significantly increased and then decreased (P=0.031). The NLR of invasive respiratory care group was significantly higher than non-invasive respiratory care group at 2nd, 3rd, and average of 1 to 3 days of life. The NLR of PPHN group was significantly higher than without PPHN group at 3rd, and average of 1 to 3 days of life. CONCLUSION: The NLR was significantly increased and then decreased in early stage of MAS and associated with the severity of MAS.