Neutrophil to lymphocyte ratio (NLR) can be easily calculated from the white cell differential count and is considered a good marker for predicting different diseases, including sepsis. Aim of the study: To study “use of neutrophils to lymphocyte ratio as an early and effective marker of sepsis in a tertiary care hospital in Chengalpattu district – a retrospective study “ Materials and methods: Cross sectional study done in the Department of Pathology, Karpaga Vinayaga Institute of Medical Sciences and Research Centre for duration of 1 year i.e. from January 2022 to January 2023. Results : Sepsis origin was from the following areas that include pulmonary (50), urinary (30), surgical (20) and abdominal (10), cutaneous (10). In our study , 80 out of 120 patients had sepsis and the remaining 40 patients had septic shock. Conclusion : Elevated levels of NLR are seen in early phase of sepsis and thus helpful in making a diagnosis, especially when obtaining microbiological culture possess limitation in terms of time and low positive rate. Late phase value of this inflammatory biomarker is also helpful in dictating the prognosis