BACKGROUND Sepsis in paediatric age group is likely due to result of sequence of disorders that is due to infection by viruses, bacteria, parasite, fungi or toxins of organisms. The outcome is improved with early recognition and resuscitation of sepsis and septic shock in the golden first few hours of PICU admission. Infection is defined as a suspected or proven (by positive culture, tissue stain or polymerase chain reaction test) infection caused by any pathogen or a clinical syndrome associated with a high probability of infection. Aims and Objectives-To find the association between PICU shock index and mortality in children with sepsis/ septic shock and to explore the cutoff values for shock index and to determine the change in shock index during the first 6 hours of PICU stay and its outcome. MATERIALS AND METHODS Study Design: Observational cohort study. Study Place: Paediatric Intensive Care Unit, Rajamirasudhar Hospital attached to Thanjavur Medical College. Study Period: 6 months period from Jan to June 2017. 50 children who presented with sepsis/ septic shock were included in the study. Children were classified as per their age as < 1 year, > 1 year-< 6 years and > 6 years. They were also grouped as sepsis, severe sepsis and septic shock as per the International Sepsis Consensus Conference definition of sepsis in 2005. Clinical parameters like heart rate and systolic blood pressure was recorded, following which shock index was calculated over 0, 1, 2, 4 and 6 hours of PICU admission and trend was noticed. Patients were finally divided into 2 groups as per outcome, i.e. survival/ death. RESULTS Data analysis was done using GraphPad Prism 5. Cutoff values of shock index were analysed using Receiver Operator Curve and their relative risk of mortality was studied. Higher values of shock index and increasing trend of shock index was associated with increased mortality. CONCLUSION SI can be a promising marker for risk of mortality in children with sepsis/ septic shock. It is simple, non-invasive and bedside clinical tool to identify high-risk children and help us keep vigilant. The obtained cutoff values indicate that higher the SI, higher is the risk of mortality.