Introduction: Bacteraemia caused by Enterobacteriaceae poses a significant threat to hospitalized patients, with rising rates of resistance to third-generation cephalo-sporins (3GC) complicating treatment efficacy. This is the first study done in Sri Lanka to assess the impact of 3GC resistance in bacteraemia patients.Objective: The aim was to study the impact of 3GC non-susceptibility on outcomes in patients with Entero-bacteriaceae bacteraemiaMethods: This is a retrospective cohort study, conducted at Sri Jayewardenepura General Hospital in Sri Lanka. Patients who had bacteraemia with Enterobacteriaceae from March 2022 to April 2024 were included. Data were collected from hospital medical records and laboratory data and by calling the patient or caregiver.Results: Of the 335 cases identified, 59.4% were bacteraemia with 3GC non-susceptible Enterobac-teriaceae (3GCNSE). Patients with 3GCNSE tended to be older with more comorbidities, and urinary infections were predominant in both groups. E. coli and K. pneumoniae exhibited high resistance rates. Significant differences were observed in 7, 14, and 30-day all-cause mortality rate, healthcare cost, and duration of hospital stay between the two cohorts. However, in regression analysis, 3GCNSE were more likely to increase healthcare cost and, underlying chronic liver disease significantly increased the severity of illness and mortality rates.Conclusions: As nearly 60% of the bacteraemia caused by Enterobacteriaceae were 3GCNS, healthcare cost was higher when managing such patients, this highlights the economic burden of antimicrobial resistance (AMR). Therefore, it is important to control the AMR in lower-middle income countries such as Sri Lanka.