Background: Pneumonia is the single biggest killer of children worldwide, accounting for nearly one in five deaths among young children, with an estimated 1.8 million deaths annually. Treatment for pneumonia during the first hours and days of onset can determine if a child lives or dies. The objective of this study is to identify determinants of delayed treatment seeking by mothers/ caregivers for under five pneumonia in Nekemt town, Oromia Regional State. Methods: The study design is a facility based unmatched case-control study. The study population was children under five years old who presented with sign and symptom of pneumonia and diagnosed to have pneumonia according to WHO criteria. The total sample size was 302 (151 cases and 151 controls) after adding 5% of nonresponsive rate. Data was collected by college nursing students. Data was first checked manually for completeness then entered coded, cleaned for errors and analyzed using SPSS version 16.0. Descriptive statistics, binary and multiple logistic regressions were employed. Result: mothers with at least secondary education were at a lower risk of delay from treatment seeking for under five pneumonia.