Introduction: Acute febrile illness (AFI) is defined as a patient with fever of 38◦C or higher at presentation or history of fever that persisted for 2–14 days with no localizing source. Fever is the main clinical symptom of various tropical infectious diseases. The objectives were to evaluate the microbiological aetiology of acute febrile illness (AFI) in pediatric patients using serological and bacterial cultures and to understand the clinical profile of acute febrile illness in pediatric patients. Methods: This is a Hospital based prospective and observational study present study emphasizes on the infective aetiologies of Acute Undifferentiated fevers with special emphasis on clinical and demographic features among patients admitted in a teaching hospital. All adult patients (≥18 years) admitted to the hospital with fever of less than 21 days duration, with temperature ≥38º C upon admission and non-detection of any specific foci of infection by history, physical examination and routine investigations were included. Results In present investigation, an aggregate of 110 patients with intense identical fever were assessed out of these 59 (53.6%) were male and 51 (46.4%) were female. In this investigation typhoid fever was the most well-known reason for undifferentiated fever (30.0%) trailed by malaria (21.7%), dengue fever (18.1%), urinary tract disease (14.5%), Acute gastroenteritis (14.5%), Pneumonia (9.0%), Bronchiolitis (4.5%), Hepatitis (1.7%) and Pharyngotonsillitis (0.9%). Conclusion: Our data showed that the etiologic spectrum of acute undifferentiated fever was widely distributed in our region. Scrub typhus was the major cause of acute undifferentiated fever next to Dengue and Enteric fever. There were a bulk of cases which were not diagnosed and put under miscellaneous aetiology of fever, this made the second largest group in our study next to the Scrub Typhus group.